would you please say that again more slowly?I don't quite---

英语请教：would you please say that again more slowly?I don't quite______you.
选择题：（备选答案）
A.follow 前边意思是你能再说一遍吗?慢点说,我跟不上你!
B.keep 就不是这个意思了,如果是话该说 keep up with you
C.know 如果是know 后边跟 know what you mean.跟从句不跟人
D.get 没怎么说的!
请问应该选哪个,为什么?我选C,可不对,又为什么?