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<select onchange='ok(this)' id=a><option>音乐<option>电影</select>
 <select id=b>
 </select>
 <script>
 function ok(objs){
 if(objs.options[objs.selectedIndex].text=="音乐")b.outerHTML="<select id=b><option selected>音乐1<option>音乐2"
 if(objs.options[objs.selectedIndex].text=="电影")b.outerHTML="<select id=b><option selected>电影1<option>电影2"
 }
 ok(a)
 </script>
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