Sorry,I can't follow you.Please say it again.当中的I can't follow you 用I don't understand.还是用I can't catch up with you .用哪个好.

Sorry,I can't follow you.Please say it again.当中的I can't follow you 用I don't understand.还是用I can't catch up with you .用哪个好.
Sorry,I can't follow you.Please say it again.当中的I can't follow you 用I don't understand.还是用
I can't catch up with you .用哪个好.

Sorry,I can't follow you.Please say it again.当中的I can't follow you 用I don't understand.还是用I can't catch up with you .用哪个好.
用I can't catch up with you比较好,因为前面的句子是I can't follow you,句子是表达我不能跟上你,请再说一遍,而catch up with这个短语也就是跟上,赶上的意思,而 don't understand是不能理解的意思,跟句子的意思不符

用第二个好啊，用第二个显示出你英语的修养，这两个都有我跟不上我不理解的意思，谢谢采纳…