问HTML和CSS新手:不显示下拉菜单

EN

ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  overflow: hidden;
  background-color: #922e2e;
  margin-top: 4px;
  margin-bottom: 4px;
}

li {
  float: left;
}

li a, span {
  display: block;
  color: white;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
}

li a:hover {
  background-color: #111;
}

#navMenu div {
  position: absolute;
 display: none;
	background-color: #7e8182;
}

#navMenu div a {
  display: block;
  width: 200px;
  height: 50px;
  background-color: #922e2e;
  color: black;
  text-align: center;
  margin-bottom: 0px;
}

#navMenu li:hover div{
	display: block;
}

<nav>
<ul id="navMenu">
<li><a href="homepage.html">Home</a></li>
<li><span>About Us</span>
<div id="about">
<a href="Darwin.html">Darwin</a>
<a href="Alex.html">Alex</a>
</div>
</li>
<li><a href="quote.html">Get a Quote</a></li>
<li><a href="contact.html">Contact Us</a></li>
</ul>
</nav>

nav
{
	margin-top:15px
}

nav ul
{
	list-style:none;
	position:relative;
	float:left;
	margin:0;
	padding:0
}

nav ul a
{
	display:block;
	color:#333;
	text-decoration:none;
	font-weight:700;
	font-size:12px;
	line-height:32px;
	padding:0 15px;
	font-family:"HelveticaNeue","Helvetica Neue",Helvetica,Arial,sans-serif
}

nav ul li
{
	position:relative;
	float:left;
	margin:0;
	padding:0
}

nav ul li.current-menu-item
{
	background:#ddd
}

nav ul li:hover
{
	background:#f6f6f6
}

nav ul div
{
	display:none;
	position:absolute;
	top:100%;
	left:0;
	background:#fff;
	padding:0
}

nav ul div li
{
	float:none;
	width:200px
}

nav ul div a
{
	line-height:120%;
	padding:10px 15px
}


nav ul li:hover > div
{
	display:block
}

<nav>
  <ul id="navMenu">
    <li><a href="homepage.html">Home</a></li>
    <li><a>About Us</a>
      <div id="about">
        <a href="Darwin.html">Darwin</a>
        <a href="Alex.html">Alex</a>
      </div>
    </li>
  <li><a href="quote.html">Get a Quote</a></li>
  <li><a href="contact.html">Contact Us</a></li>
  </ul>
</nav>