angularjs select 默認選中option

下面代碼用html實現了angular1.x  select默認選中option   （初始狀態效果如下）

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<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全年計划完成情況.svg" class="responsive-img"/></i><span>發電量統計</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;">--請選擇--
            </option>
            <option value="directive1" ng-selected="true">柱狀圖</option>
            <option value="directive3">熱圖</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">熱圖
                <solar-calheatmap options="vm.options"
                                  style="display :block;position:absolute;top:36px;left:0;right:0;bottom:0;"></solar-calheatmap>
            </div>
        </div>
    </div>
</div>