阅读此DropDownList文章：

DropDownList [ ^ ]



阅读如何链接，选择重定向时的相关框架/版本。



这应该让你快速了解如何使用DropDownList。

Have a read of this DropDownList article:
DropDownList[^]

Read the "How to" links, select the relevant framework/version when redirected.

That should get you up to speed on how to use a DropDownList.