为什么我弄a:hover{text-decoration:underline;}下划线不出来呢?

为什么我弄a:hover{text-decoration:underline;}下划线不出来呢?

.experts_cont li{width:300px; height:360px; float:left;list-style:none;text-decoration:none; margin-right:25px; margin-top:20px;}
.experts_cont li a:hover{text-decoration:underline;}
.experts_box{border-top:#c9c9ca solid 7px;width:275px; height:358px; float:left; margin-left:23px; margin-right:20px;}
.experts_tittle{font-family:"兰亭刊黑"; font-size:14px; color:#000; padding-top:30px; text-align:center;}
.experts_img{width:277px; height:163px; padding-top:39px;}
.experts_content{font-family:"兰亭刊黑"; font-size:12px; padding-top:10px;color:#000; text-indent:2em; width:278px;}
.experts_tittle a:hover{text-decoration:underline;}