伪类:悬停在IE7中不起作用

我有这么简单的代码:

  
Foo
  

    

      

        Bar
      
        
    
  

这个CSS:

.div1{
  position: relative;
}
.div1 .div3 {
  position: absolute;
  top: 30px;
  left: 0px;
  width: 250px;
  display: none;
}
.div1:hover .div3 {
  display: block;
}
.div2{
  width: 200px;
  height: 30px;
  background: red;
}
.div4 {
  background-color: green;
  color: #000;  
}
.div5 {}