angularjs select 默认选中option

下面代码用html实现了angular1.x  select默认选中option   （初始状态效果以下）

--------------------------------------------------------<div class="row">    <div class="col s12">        <div class="solar-icon-title"><i class="material-icons left"><img                src="solar/res/logo-icon/60-40整年计划完成状况.svg" class="responsive-img"/></i><span>发电量统计</span>        </div>        <select ng-model="myVar"                style="display:block;position:absolute;right:10px;top:5px;width:70px;font-size:1rem;height:24px;margin:0;padding:0;">            <option value="" disabled="disabled" style="display:none;">--请选择--            </option>            <option value="directive1" ng-selected="true">柱状图</option>            <option value="directive3">热图</option>        </select>        <div ng-switch="myVar">            <div ng-switch-default="directive1">                <chart-bar options="vm.bar"                           style="display:block;position:absolute;top:36px;left:0;right:0;bottom:0;"></chart-bar>            </div>            <div ng-switch-when="directive3">热图                <solar-calheatmap options="vm.options"                                  style="display :block;position:absolute;top:36px;left:0;right:0;bottom:0;"></solar-calheatmap>            </div>        </div>    </div></div>