如何将类应用于ng-options

Question

我想应用一个类来选择angularjs中的框选项。

<div ng-controller="ExController" ng-init="init([{name:'name1',city:'city1'},{name:'name2',city:'city2'},{name:'name3',city:'city3'}])">
<select ng-model="selectedCustomer" ng-options="cust.name + '-' + cust.city for cust in customers | orderBy:'name'"></select>
</div>

我尝试使用ng-class来选择标签，但该类未应用于选项。