How can I set the selected value in dropDownList Yii

[heading title=”How can I set the selected value in the following statement ” type=”h2″ font_size=”” margin_top=”30″ margin_bottom=”30″ color=””]
[code inline=”true” scrollable=”true”]$form->dropDownList($model, ‘pair’, array(“2″=>”2”, “3”=>”3″,”4″=>”4″, “5”=>”5″,”6″=>”6″,”7″=>”7″, “8”=>”8″, ‘9’=>’9′, “10”=>”10″, “11”=>”11″, “12”=>”12″, “13”=>”13″, “14”=>”14″, ’15’=>’15’, ’20’=>’20’, ’25’=>’25’, ’30’=>’30’, ’35’=>’35’, ’40’=>’40’ , ’45’=>’45’ , ’50’=>’50’, ’55’=>’55’), array(‘class’=>’form-control’, ‘options’ => array(‘4’=>array(‘selected’=>true)),))[/code]