vue2.0 下拉框默认标题设置方法

ERROR in ./~/vue-loader/lib/template-compiler.js?id=data-v-c231dfa2!./~/vue-loader/lib/selector.js?type=template&index=0!./src/components/second.vue
template syntax error <select v-model="selected">:
inline selected attributes on <option> will be ignored when using v-model. Declare initial values in the component's data option instead.

<template>
 <select v-model='selected' @click="ss()">
 <option v-for="(option,index) in options" v-bind:value="option.value" :disabled="option.disabled">
 {{ option.text }}{{index}}{{option.disabled}}
 </option>
 </select>
 <span>Selected: {{ selected }}</span>
</template>
<script>
 export default{
 name: 'second',
 data(){
 return {
 selected: 'sex', // 比如想要默认选中为性别，那么就把他的value值设置为'sex'
 options: [
 {text: '性别', value: 'sex', disabled: ''}, //每个选项里面就不用在多一个selected 了
 {text: '男', value: '1'},
 {text: '女', value: '2'}
 ]
 }
 },
 methods: {
 ss: function () {
 this.options[0].disabled = disabled;
 },
 }
 }
</script>