form_dropdown allowing to select only one item

[eluser]dinisptc[/eluser]
form_dropdown allowing to select only one item

Code:

<?php                                
              
                $js = 'id="contractorCompany"';
              
                echo form_dropdown('companyUID', $companies, set_value('companyUID', $companies),$js);
                                                
                ?>

we have to issues with the form dropdown

one : its showing opened like a list view
two: allows to select multiple items , but only one its selected maybe the last one

how to allow the selection of only one item
how to show the dropdown closed like a combo_box


thanks