您需要在 select 元素上设置一个 onchange 事件
<select onChange="window.location = '//' + this.value + '.graphic.com';">
<option value="" selected>Pick a Website</option>
<option value="City1">Google</option>
<option value="City2">YouTube</option>
<option value="City3">Stack Overflow</option>
</select>
如果您希望浏览器打开一个新窗口:
<select onChange="window.open('//' + this.value + '.graphic.com');">
<option value="" selected>Pick a Website</option>
<option value="City1">Google</option>
<option value="City2">YouTube</option>
<option value="City3">Stack Overflow</option>
</select>