AngularJS - How to add placeholder text to dropdown

I am new to angularjs. I want to add a placeholder to my dropdown. I am not hard coding my dropdown values, it's coming from some where. Can you tell me where i did mistake. ``` <div class="row form-group"> <label class="col-md-3">Action<span style="color: #b94a48">*</span></b></label> <div class="col-lg-3 col-md-7" style="padding: 0px;"> <div class="dropdown select" style="width: 100%;"> <select name="wlOrdActType" class="dropdown multiple" placeholder="-- Please Select --" ng-model="wlOrdActType" ng-options="obj.name as obj.name for obj in ordertypeList" style="width: 100%;"> <option></option> </select> </div> </div> </div> ``` Here every thing is working. But placeholder is not place on the dropdown