AngularJS ng-options for html select element

ng-options-select.html

              <select
                name="customer_id"
                id="customer_id"
                class="text"
                ng-model='filtro.estado'
                ng-click="selectItem('estado', filtro.estado, $event)"
                ng-options="estado as estado for estado in listas.estados">
                <option value="">Selecione</option>
              </select>

              <select
                name="customer_id2"
                id="customer_id2"
                class="text"
                ng-model='filtro.estado2'
                ng-click="selectItem('estado', filtro.estado2, $event)"
                ng-options="v as v for (k,v) in listas.estados">
                <option value="">Selecione</option>
              </select>