问题补充：
-----buy a ring for her?A Why don you B Lets C What about D Would you mind
答案：
A表建议：why don you do sth.
而：Lets do sth.后面用句号,what about / would you mind + doing
不明白的再问哟,请及时采纳,多谢!
======以下答案可供参考======
供参考答案1:
选A.Why don you
供参考答案2:
Would you mind buy a ring for her?正解答案：D
供参考答案3:
A供参考答案4:
选择A，Why don you buy a ring for her ？为什么不给她买个戒指？
疑问句很显然不用Lets ，What about 中因为about是介词，所以后面要接—ing ，Would you mind 也应该接—ing 才对。
供参考答案5:
A Why don you
供参考答案6:
选A Why don you 后加动词原形，为何不。。。？表建议
Lets 后加动词原形 让我们 祈使句 表建议
What about 后加动词ing形式 。。。怎么样？表建议
Would you mind 后加动词ing形式，你介 意。。吗？表征询。据题意可知选项A更恰当
