<html><head><script>function getIndex() { document.getElementById("demo").innerHTML = document.getElementById("mySelect").selectedIndex;}</script></head><body><form>选择你最喜欢的水果：<select id="mySelect"> <option>苹果</option> <option>橙</option> <option>菠萝</option> <option>香蕉</option></select><br><br><input type="button" onclick="getIndex()" value="显示所选选项的索引"></form><p id="demo"></p></body></html>