Hi, I hope i am in the right place. I need help as soon as possible of dynamically displaying html form elements from anothe form all in same php page

I want to be able to select an option from a select list and have it pass the value of the variable to another select list and have the second select list displayed with the first one still displayed.

I want to be able to display a third select list from the last displayed select list.

this is the code that i have tried, which works, but the second select list disappears when i make a selection.

<?php
$result = $_REQUEST['sel']; ?>

<form name="mfrm" method="POST" target="_self" action="try.php">
<select name="sel" size="2" onChange="submit()">
<option name="">select</option>
<option name="1">Population
<option name="2">Correlation
</select>
</form>



<?php if ($result == 'Population') { ?>

<form name="nfrm" method="GET">
<select name="selx" onChange="submit()">
<option name="">select</option>
<option name="3">3Population</option>
<option name="4">4Correlation</option>
</select>
</form>

<?php } ?>


Thanks
wokoci