简单的英语句子正误，谢谢！

Now,who can guess what this ad is about ?
是正确的。who can guess 后加宾语便是一个完整的句子。this ad is about 只是对WHAT的补充说明，只能用一般的语序。

第二句

c

选第三个。
Who can guess已经是主句了，后面应该用正常的主谓宾结构，what提前了。
个人意见~

Now,who can guess what's this ad about?