try this:<html><head>
<script>
function show(u)
{
if(u=="t1"){f1.t1.style.visibility="visible"}
else if(u=="t2"){f1.t2.style.visibility="visible"}
else if(u=="t3"){f1.t3.style.visibility="visible"}
}
</script>
</head><body><form name="f1" method="POST" action="--WEBBOT-SELF--">
<p>
<select size="1" name="D1" onchange="show(this.value)">
<option selected >select</option>
<option value="t1">1</option>
<option value="t2">2</option>
<option value="t3">3</option>
</select></p>
<p>
<input type="text" name="t1" size="20" style="visibility:hidden" value="111"></p>
<p>
<input type="text" name="t2" size="20" style="visibility:hidden" value="22222"></p>
<p>
<input type="text" name="t3" size="20" style="visibility:hidden" value="33333"></p>
<input type="button" onclick="">
</form></body></html>
<script>
function show(u)
{
if(u=="t1"){f1.t1.style.visibility="visible"}
else if(u=="t2"){f1.t2.style.visibility="visible"}
else if(u=="t3"){f1.t3.style.visibility="visible"}
}
</script>
</head><body><form name="f1" method="POST" action="--WEBBOT-SELF--">
<p>
<select size="1" name="D1" onchange="show(this.value)">
<option selected >select</option>
<option value="t1">1</option>
<option value="t2">2</option>
<option value="t3">3</option>
</select></p>
<p>
<input type="text" name="t1" size="20" style="visibility:hidden" value="111"></p>
<p>
<input type="text" name="t2" size="20" style="visibility:hidden" value="22222"></p>
<p>
<input type="text" name="t3" size="20" style="visibility:hidden" value="33333"></p>
<input type="button" onclick="">
</form></body></html>
<script>
function showit(n){
aa.style.display='none';
bb.style.display='none';
cc.style.display='none';
eval(n).style.display='';
}
</script>
<form>
<select onchange=showit(this.options[selectedIndex].value)>
<option>请选择</option>
<option value=aa>第一个</option>
<option value=bb>第二个</option>
<option value=cc>第三个</option>
</select>
</form>
<div id=aa style="display=none">
<input type=text value=第一个 size=10>
</div>
<div id=bb style="display=none">
<input type=2 value=第二个 size=20>
</div>
<div id=cc style="display=none">
<input type=text value=第三个 size=30>
</div>
_________________________________________________________
测试通过。