how do i add id in this codeigniter select options

how do i add id in this codeigniter select op开发者_Go百科tions

echo form_dropdown('selling', $ex_rates);?>

Read the userguide.

If you would like the opening to contain additional data, like an id attribute or JavaScript, you can pass it as a string in the fourth parameter:

$js = 'id="shirts" onChange="some_function();"';

echo form_dropdown('shirts', $options, 'large', $js);