ysm-design on "customise search"

Hi.
I made a kind of search box, that my search have 4 Dropdown field with some categorise.

my code:

<form method="get" id="searchform" action="<?php bloginfo('home'); ?>/">
<?php wp_dropdown_categories( 'hide_empty=0&child_of=3&show_option_all=Kind' ); ?>
<?php wp_dropdown_categories( 'hide_empty=0&child_of=22&show_option_all=Value' ); ?>
<?php wp_dropdown_categories( 'hide_empty=0&child_of=54&show_option_all=Weight' ); ?>
<?php wp_dropdown_categories( 'hide_empty=0&child_of=65&show_option_all=width' ); ?>
<input type="submit" id="searchsubmit" value="Search" />
</form>

when a user select 4 field, and then Click on Search, my search form work very well and show the result good,
But when the user select 3 or 2 or 1 field, my form do not work well and dont show the result.

what can i do?