dropdownlist

how to select multiple choice from dropdownlist in yii?

here’s my code:

[center]<div class="row">

		      <div class="input_box">


			        <label><?php echo $form->labelEx($model,'fruit'); ?></label>


			        <?php echo $form->dropDownList($model,'fruit',array('apple'=>'apple','mango'=>'mango','pineapple'=>'pineapple')); ?> 


					<?php echo $form->error($model,'fruit'); ?> 


               </div>


		 </div>[/center]

 <?php echo $form->dropDownList($model,'fruit',

          array('apple'=>'apple','mango'=>'mango','pineapple'=>'pineapple'),

          array('size'=>'30')); ?>