51help TIY
码：
<html> <head> <script type="text/javascript"> function selectOrange() { document.getElementById("orange").selected=true; } </script> </head> <body> <form> <select> <option id="apple">苹果</option> <option id="orange">桔子</option> <option id="pineapple" selected="selected">菠萝</option> <option id="banana">香蕉</option> </select> <br /><br /> <input type="button" onclick="selectOrange()" value="选择桔子"> </form> </body> </html>
查看结果: