菜单

AP准备

AP微积分

美国历史

保证，提高您的SAT或ACT分数。开始你的1周免费试用Magoosh SAT PREP或者你1周免费试用Magoosh法案准备今天！

分享

鸣叫

别针

#llc_comments{display:none;}#llc-comments-loader img{display:none;}#llc_comments_button{display:none;}#llc_comments > h3{display:none;}#llc_comments #comments{display:block;}#header .searchform button:active{-webkit-box-shadow:none !important;box-shadow:none !important;}.search_main.searchform-wrap.active,.search_main.searchform-wrap.inactive{width:280px;right:-25px;float:right;position:relative;top:-80px;}.search_main.searchform-wrap.active form.searchform,.search_main.searchform-wrap.inactive form.searchform{border-top:#fff;border-left:#fff;border-right:#fff;float:left;width:255px;margin-top:0;}.search_main.searchform-wrap.active button.submit,.search_main.searchform-wrap.inactive button.submit{left:0;}.search_main.searchform-wrap.active button.searchform-close,.search_main.searchform-wrap.inactive button.searchform-close{border:none;font-size:20px;color:#7e8280;position:relative;left:-25px;width:20px;}.search_main.searchform-wrap.active input,.search_main.searchform-wrap.inactive input{padding-left:40px;}.search_main.searchform-wrap.inactive{opacity:0;transition:all .5s ease-in-out;-moz-transition:all .5s ease-in-out;-webkit-transition:all .5s ease-in-out;}.search_main.searchform-wrap:focus{opacity:1;top:-65px;}.search_main.searchform-wrap.active{opacity:1;top:-65px;transition:all .5s ease-in-out;-moz-transition:all .5s ease-in-out;-webkit-transition:all .5s ease-in-out;}.search_main.searchform-wrap.active:focus{opacity:0;transition:opacity .5s ease-in-out;-moz-transition:opacity .5s ease-in-out;-webkit-transition:opacity .5s ease-in-out;}ul.nav{margin-right:0 !important;}#navigation.col-full{max-width:1180px !important;width:1180px !important;}#navigation{border:none !important;margin-top:35px;background:#fff !important;}ul#main-nav li{border:none !important;}ul#main-nav li a{font-family:tondo,sans-serif !important;border:none;font-size:16px;}#navigation ul#main-nav li:hover > a,#navigation ul#main-nav li:focus > a,#navigation ul#main-nav li:active > a{border:1px solid #d1d3d4;}ul#main-nav > li > a{padding:10px !important;border:1px solid #fff;border-radius:4px !important;font-weight:700;}#navigation .nav li.menu-item-has-children{display:flex;}#navigation .nav li.menu-item-has-children > a::after{content:" " !important;font-family:"FontAwesome";font-size:.857em;font-style:normal;font-weight:normal;speak:none;}#navigation .nav li.menu-item-has-children > a:hover::after{visibility:hidden;}#navigation ul.nav > li:hover{background:#fff !important;}#navigation ul.nav > li > a:hover,#navigation ul.nav > li > a:active,#navigation ul.nav > li > a:focus{background:#fff !important;}#navigation ul.sub-menu{background:#fff !important;line-height:30px;width:auto;padding:0;border-radius:4px !important;}#navigation ul.sub-menu li{font-family:tondo,sans-serif !important;}#navigation ul.sub-menu li a{line-height:25px;border:0 !important;}#navigation ul.sub-menu li a:hover{color:#fff !important;background-color:#4c2477 !important;text-decoration:none !important;border:0 !important;}#navigation .search-wrap{float:left;margin-left:40px;position:relative;top:-2px;}#navigation .log-button{opacity:0;float:right;}#navigation .log-button a{background-color:#4c2477 !important;text-transform:none;border:2px solid #4c2477 !important;}#navigation .log-button a:hover,#navigation .log-button a:focus,#navigation .log-button a:active{color:#4c2477 !important;background:#fff !important;}#navigation button.fa-search{opacity:0;}.search_sticky.searchform-wrap.inactive{opacity:0;visibility:hidden;}.navigation-wrap.sticky{position:fixed;top:0;z-index:100;background:#fff;box-shadow:0 4px 2px -2px #d1d3d4;}.navigation-wrap.sticky #navigation{margin-top:12px;margin-bottom:12px;}.navigation-wrap.sticky #navigation ul li:first-child a{padding-left:0 !important;}.navigation-wrap.sticky #navigation button.fa-search,.navigation-wrap.sticky #navigation .log-button{opacity:1;}.navigation-wrap.sticky #navigation .search-log{display:flex;}.navigation-wrap.sticky #navigation .search-log::after{clear:both;content:"";display:table;}.navigation-wrap.sticky #navigation .search-log .button{white-space:nowrap;}.navigation-wrap.sticky .log-button{opacity:1;}.outer-search-wrap{visibility:hidden;position:fixed;width:100%;max-width:1180px;margin:0 auto;z-index:90;top:0;transition:all .5s ease-in-out;-moz-transition:all .5s ease-in-out;-webkit-transition:all .5s ease-in-out;}.inner-search-wrap{width:280px;float:right;}.search_sticky.searchform-wrap.active,.search_sticky.searchform-wrap.inactive{width:100%;float:right;position:relative;border-bottom:1px solid #d1d3d4;top:-130px;padding:15px 0;background-color:#fff;}.search_sticky.searchform-wrap.active form.searchform,.search_sticky.searchform-wrap.inactive form.searchform{border-top:#fff;border-left:#fff;border-right:#fff;float:left;width:255px;margin-top:0;}.search_sticky.searchform-wrap.active button.submit,.search_sticky.searchform-wrap.inactive button.submit{left:0;}.search_sticky.searchform-wrap.active button.searchform-close,.search_sticky.searchform-wrap.inactive button.searchform-close{border:none;font-size:20px;color:#7e8280;position:relative;left:-25px;width:20px;}.search_sticky.searchform-wrap.active input,.search_sticky.searchform-wrap.inactive input{padding-left:40px;}.searchform.trigger{border:none;}.searchform button:active{-webkit-box-shadow:none !important;box-shadow:none !important;}.search_sticky.searchform-wrap.inactive{opacity:0;transition:all .5s ease-in-out;-moz-transition:all .5s ease-in-out;-webkit-transition:all .5s ease-in-out;}.search_sticky.searchform-wrap:focus{opacity:1;top:-90px;}.search_sticky.searchform-wrap.active{opacity:1;top:65px;visibility:initial;transition:all .5s ease-in-out;-moz-transition:all .5s ease-in-out;-webkit-transition:all .5s ease-in-out;}.search_sticky.searchform-wrap.active:focus{opacity:0;transition:opacity .5s ease-in-out;-moz-transition:opacity .5s ease-in-out;-webkit-transition:opacity .5s ease-in-out;}.mobile-menu-icon{position:fixed;right:2rem;top:2rem;}.mobile-menu-icon::after{color:#30b57e;cursor:pointer;font-size:2rem;}.main-menu-item.menu-item-has-children{position:relative;}.mobile-submenu-icon{font-size:2rem;position:absolute;right:1rem;top:.5rem;}.mobile-submenu-icon::after{cursor:pointer;}.mobile-menu-wrap{background-color:#fff;display:block;left:0;margin-bottom:1rem;overflow-y:auto;position:fixed;top:0;transform:translateX(-100%);transition:transform .2s linear .1s;width:75%;z-index:1000;}.mobile-menu-wrap a:link,.mobile-menu-wrap a:visited{color:currentColor;display:inline-block;padding:0 1em;}.mobile-menu-wrap li{border-bottom:1px solid #d1d3d4;font-size:18px;line-height:24px;padding:.5em 0;}.mobile-menu-wrap .menu-main-menu-container{max-height:90vh;overflow-y:scroll;}.mobile-menu-wrap .search-log{display:block;}.mobile-menu-wrap .log-button,.mobile-menu-wrap .signup-button{display:inline-block;margin:1em;}.mobile-menu-wrap .log-button a,.mobile-menu-wrap .signup-button a{background-color:#4c2477;padding:.5em 1em;}.mobile-menu-wrap .sub-menu{display:none;}.mobile-menu-wrap .search_main.searchform-wrap.active{display:block;float:none;margin:1em;right:auto;top:auto;}@media only screen and (max-width: 1200px){.navigation-wrap{display:none !important;}#header.col-full{max-width:1023px !important;width:1023px !important;}#header{max-width:1023px;width:1023px;}#header h1.site-title a{font-size:2em;}#header .site-title sup{top:-1.2em;}#header .branding{width:100%;position:fixed;z-index:1000;background:#fff;top:0;padding:15px 0;margin-left:-2px;}#header h2.site-long-description{display:none;margin-left:30%;z-index:1000;}a.responsive-menu-custom-button{background-color:#4c2477;color:#fff !important;border:2px solid #4c2477;padding:.327em 1em !important;border-radius:4px;}a.responsive-menu-custom-button:hover,a.responsive-menu-custom-button:active,a.responsive-menu-custom-button:focus{text-decoration:none;color:#4c2477 !important;background-color:#fff;}.search-log,.search_main.searchform-wrap.inactive,.search_main.searchform-wrap.active{display:none;}.mobile-menu-icon{z-index:1000;}.mobile-menu-icon::after{content:"☰";speak:none;}#mobile-menu-toggle:checked + .mobile-menu-icon::after{content:"✕";}#mobile-menu-toggle:checked ~ .mobile-menu-wrap{transform:translateX(0);}.mobile-submenu-icon::after{content:"▾";speak:none;}.mobile-submenu-toggle:checked + .mobile-submenu-icon{background-color:#4c2477;color:#fff;transform:rotate(180deg);}.mobile-submenu-toggle:checked ~ .sub-menu{display:block;text-indent:1em;}.mobile-submenu-toggle:checked ~ .sub-menu li:last-child{border-bottom:none;}.search-wrap .search-form-icon{font-family:"FontAwesome";font-size:18px;}.search-wrap .search-form-icon::after{content:"";speak:none;}.search_mobile .searchform,.search_mobile .searchform{border-left:2px solid #f1f3f1;border-right:2px solid #f1f3f1;border-top:2px solid #f1f3f1;margin-left:2rem;width:unset;}}@media only screen and (max-width: 1050px){#header.col-full{max-width:900px !important;width:900px !important;}#header{max-width:900px;width:900px;}#header h1.site-title a{font-size:1.8em;}#header h2.site-long-description{width:40%;}}@media only screen and (max-width: 910px){.site-logo{margin-left:0px;}#header.col-full{max-width:800px !important;width:100% !important;}#header{max-width:800px;width:800px;}}@media only screen and (max-width: 767px){.nav-toggle{display:none !important;}#header{border-bottom:none !important;}#header h2.site-long-description{display:none;}#header h1.site-title a{display:inline;font-size:1.4em;line-height:1.2;margin-top:0;}#header .site-title{max-width:85%;}#header .site-title sup{top:-1em;}#header .site-logo img{margin-top:10px;}button#responsive-menu-pro-button{top:15px !important;}}@media only screen and (max-width: 460px){#header .branding{margin-left:-6px;}}