代码如下：

HTML

<div>
  <md-input-container>
    <md-select multiple ng-model="ctrl.likedAnimals" placeholder="please select">
      <md-option ng-repeat="a in ctrl.animals" value="{{a}}">{{a}}</md-option>
    </md-select>
  </md-input-container>
</div>

JS

(function () {
  'use strict';
  angular
      .module('MyApp')
      .controller('AppCtrl', function($scope) {
        this.likedAnimals = ["mouse", "dog"];
        this.animals = ["mouse", "dog", "cat", "bird"];
  });
})();