Drop Down List Creates In Optgroup.

Hi,

I am trying to create dropdown list but the options are displayed as optgroup which I dont want, how can I solve this.

This is what I have done in the model:

public function getbirthdayOptions()
	{            
	  return array('' => 'Select Day',range(0, 12));
	}[

Can anyone help me on this.
I have just started learning yii.

Thanks