How to make anchor links underline only when mouseover

<head> a { text-decoration:none } <script type="text/javascript">var switchTo5x=true;</script> <script type="text/javascript" src="https://ws.sharethis.com/button/buttons.js"></script> <script type="text/javascript">stLight.options({publisher: "83cf11a5-04b0-47d5-b5d0-fecf32207997", doNotHash: false, doNotCopy: false, hashAddressBar: false});</script> </head> <body> <a href="http://www.google.com" OnMouseOut="this.style.textDecoration='none'" OnMouseOver="this.style.textDecoration='underline'" > link</a> </body> </html>