为什么一加a标签，布局就错位
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml" lang="zh-CN"><head><title>测试a标签</title><meta http-equiv="Content-Type" content="text/html; charset=utf-8" /><meta name="description" content="" /><meta name="keywords" content="" /><style type="text/css">* { margin:0; padding:0; border:0;}#container { width:990px; height:370px; margin:auto;}#hot { width:990px; height:370px; background:blue;}#ad { float:left; width:330px; height:370px;}#exceting { float:left; width:391px; height:370px;}#right-bar { float:right; width:250px; width:370px;}</style></head> <body> <div id="container"> <div id="hot"> <div id="ad"> <a id="ad-a" href="#"><a> </div> <div id="exceting"> <div id="cell1"><a href="#">ww</a></div> <div id="cell2">ss</div> </div> <div id="right-bar"> <div id="right-top"> </div> <div id="right-bottom"></div> </div> </div> </div> </body></html>