angularjs 获取默认选中的单选按钮的value方法

<span style="font-size:18px;"><div ng-controller="testCtrl"> 
 <div > 
  <label > 
   <input type="radio" value="Normal" ng-model="level" name="level" 
   >一般 
  </label> 
  <label > 
   <input type="radio" value="Important" ng-model="level" name="level" 
     ng-checked="true" 
   >重要 
  </label> 
  <label > 
   <input type="radio" value="Urgent" ng-model="level" name="level" 
   >紧急 
  </label> 
 
 
 </div> 
  <div> {{ level }}</div>    //显示单选按钮选中的value 
</div></span>