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				<?php wp_dropdown_categories($select_cats); ?>
				<?php  $select_cats = wp_dropdown_categories( array( 'echo' => 0, 'taxonomy' => 'category', 'include' => '16,21' ) );
					 $select_cats = str_replace( "name='cat' id=", "name='cat[]' multiple='multiple' id=", $select_cats );
					 echo $select_cats; ?>