​x
 
<html>
<head>
<script type="text/javascript">
function selectOrange()
  {
  document.getElementById("orange").selected=true;
  }
</script>
</head>
​
<body>
<form>
请选择您喜欢的水果：
<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>
​