AngularJs的ng-options 的value错误？

<div ng-controller="CityController">
    <select ng-model="city" ng-options="city.name for city in cities">
        <option value="">Choose City</option>
    </select>
    Best City: {{ city.name }}
</div>

<script type="text/javascript">
    var testApp = angular.module("testApp", []);
    testApp.controller("CityController", function($scope){
        $scope.cities = [
            {name: 'Seattle'},
            {name: 'San Francisco'},
            {name: 'Chicago'},
            {name: 'New York'},
            {name: 'Boston'}
        ];
    });
</script>

渲染完后：

<select ng-model="city" ng-options="city.name for city in cities" class="ng-pristine ng-valid ng-touched">
    <option value="" class="" selected="selected">Choose City</option>
    <option label="Seattle" value="object:3">Seattle</option>
    <option label="San Francisco" value="object:4">San Francisco</option>
    <option label="Chicago" value="object:5">Chicago</option>
    <option label="New York" value="object:6">New York</option>
    <option label="Boston" value="object:7">Boston</option></select>

为什么我渲染出来value的值是错误的，而且多了个label的属性，书上渲染出来是正确的jsbin上的例子？？？

---

你直接取ng-model取值看看能取到正确的值吗？代码没看出来哪错了。