有关“联动下拉菜单”！！！！应该不是很简单

<SCRIPT language="javascript">
function hide(val)
{
    if(val == "A")
    {
        sel1.style.display = "";
        txt1.style.display = "none";
    }
    else
    {
        sel1.style.display = "none";
        txt1.style.display = "";
    }
}
</SCRIPT>
</HEAD><BODY>
<SELECT id="sel" style="width:70px" onChange="hide(this.value)">
  <OPTION value="A" selected>A</OPTION>
  <OPTION value="B">B</OPTION>
</SELECT>
<SELECT id="sel1" style="width:70px"></SELECT>
<INPUT id="txt1" style="display:none">
</BODY>

解决方案 »

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<script>
function check(st){
if(st.value=="a"){
div1.style.display="block"
div2.style.display="none"
}
if(st.value=="b"){
div2.style.display="block"
div1.style.display="none"
}
}
</script><select onchange=check(this)>
  <option value=a>a
  <option value=b>b
</select>
<div id=div1 style="display:none;">
  <select></select>
</div>
<div id=div2 style="display:none;">
  <input type=text>
</div>