1. 复选框 组
```
<input type="checkbox" v-model="flagN" value="1">A
<input type="checkbox" v-model="flagN" value="2">B
<input type="checkbox" v-model="flagN" value="3">C
<span>{{flagN}}</span>
flagN: []
```
2. 单选框 组
```
<input type="radio" v-model="flagN" value="1">A
<input type="radio" v-model="flagN" value="2">B
<input type="radio" v-model="flagN" value="3">C
<span>{{flagN}}</span>
flagN: '1'
```
3. 下拉框 组
```
<select v-model="select">
<option v-for="(item,pos) in items" :value="item.value" :key="pos">{{item.text}}</option>
</select>
<span>{{select}}</span>
select: 'b'
```
