select联动，写的代码有些不对

Question

document.all("text1").options.value=="bbb"

Answer 1

if(document.getElementById('text1').selectedIndex==2)   //  改成这样
document.getElementById('s1').style.display = "block";
document.getElementById('s1').style.display = "none";

Answer 2

<SCRIPT LANGUAGE="JavaScript">
<!--
function showS1() {
if(document.getElementById('text1').selectedIndex==2)
{
document.getElementById('s1').style.visibility = "visible";
}
else
{
document.getElementById('s1').style.visibility = "hidden";
}
}
//-->
</SCRIPT><SELECT NAME="text1" onchange="showS1()">
<option></option>
<option id="aaa">aaa</option>
<option id="bbb">bbb</option>
<option id="ccc">ccc</option>
</SELECT><SELECT NAME="s1" style="visibility:hidden">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</SELECT>

Answer 3

<SCRIPT LANGUAGE="JavaScript">
<!--
function showS1() {
var select = document.getElementById("text1");
if(select.options[select.selectedIndex].text=="bbb"){ 
document.getElementById("s1").style.visibility = "visible";
alert("aaa");
}}
</SCRIPT><SELECT NAME="text1" onClick="showS1()">
<option></option>
<option id="aaa">aaa</option>
<option id="bbb">bbb</option>
<option id="ccc">ccc</option>
</SELECT><SELECT NAME="s1" style="visibility:hidden">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</SELECT>

Answer 4

<SCRIPT LANGUAGE="JavaScript">
<!--
function showS1() {
var select = document.getElementById("text1");
if(select.options[select.selectedIndex].text=="bbb"){ 
document.getElementById("s1").style.visibility = "visible";
}
else{
document.getElementById("s1").style.visibility = "hidden";
}}
</SCRIPT>