angularjs的单选框+ng-repeat的实现方法

<div class="container" width="1900px" data-ng-controller="QuestionSettingCtrl">
 <div class="text-center" data-ng-repeat="item in items">
 <table>
 <tr><td data-ng-bind="$index+1 +'、 '+item.test" colSpan="4"></td></tr>
 <tr><td> </td></tr>
 <tr>
 <td><input type="radio" value="A" data-ng-model="answer[$index]" />A <span data-ng-bind="item.op1"></span> </td>
 <td><input type="radio" value="B" data-ng-model="answer[$index]" />B <span data-ng-bind="item.op2"></span> </td>
 <td><input type="radio" value="C" data-ng-model="answer[$index]" />C <span data-ng-bind="item.op3"></span> </td>
 <td><input type="radio" value="D" data-ng-model="answer[$index]" />D <span data-ng-bind="item.op4"></span> </td>
 </tr>
 </table>
 <br>
 <br>
 </div>
 <div class="text-center"><button class="btn btn-primary" style="margin: 0 auto;" data-ng-click="submit()">提交</button></div>
 <br><br><br><br>
</div>

app.controller('QuestionSettingCtrl',function($scope, $http){
 $scope.answer = new Array(30);
 $http({
 url :　"/getexamquestions",
 method : "post",
 params : {
 'account' : 30
 }
 }).success(function(res){
 $scope.items=res;
 });
 
 $scope.submit = function(){
 $http({
 url :　"/submitanswer",
 method : "post",
 params : {
 'answer' : $scope.answer
 }
 }).success(function(res){
 alert("你做对了"+res+"题!");
 });
 }
});