denis_kontarev,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.hidden{
display:none;
}
.hidden.chosen{
display:block;
}
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
$('#choice').change(function(){
$('div.hidden').removeClass('chosen').eq(this.value).addClass('chosen')
})
});
</script>
</head>
<body>
<select id="choice">
<option value="0" selected>one</option>
<option value="1">two</option>
<option value="2">three</option>
</select>
<div class="hidden chosen"> some codes <xmp><script>jquery 1 here...</script></xmp></div>
<div class="hidden"> some codes <xmp><script>jquery 2 here...</script></xmp></div>
<div class="hidden"> some codes <xmp><script>jquery 3 here...</script></xmp></div>
</body>
</html>