如何为特定项启用div ???使用angularjs和bootstrap

Question

<div class="form-group" ng-class="{'active':field == 'state'}" >
<div class="col-xs-4 pad-none" ng-class="{'has-error has-feedback' : authorNoteForm.contactPerson.$valid && authorNoteForm.notesState.$invalid && submitted }">
                <div class="col-xs-4" >
                    <label class="control-label muted" for="notesState">State</label>
                </div>
                <div class="col-xs-8 pad-none">
                    <input type="text" class="form-control" id="notesState" name="notesState" ng-change="valueChangesMade()" ng-model="data.correspondenceAddress.state" ng-readonly="previewMode" ng-focus="field='state'" required>
                    <span class="glyphicon glyphicon-warning-sign form-control-feedback" ng-show="authorNoteForm.contactPerson.$valid && authorNoteForm.notesState.$invalid && submitted"></span>
                </div>
            </div>
</div>

我有国家的div。它应该仅适用于美国和加拿大这两个国家。我无法找到解决方案。你可以帮我吗