Greg: Hi ,Karen. I have tickets to a concert at Carnegie Hall. It starts at 8:00.

Karen: Hmmm... ___________

A. Sure, but I have to prepare for the exam.

B. Thank you all the same.

C. Leave it to me, I assure you.

D. I'm afraid I can't make it by then.

D【解析】选项A是矛盾的回答。Sure表示接受，但but I have to prepare for the exam又是拒绝的回答；Thank you all the same是对他人因没帮上忙而道歉的回答，表示“尽管如此。也要谢谢您”的意思；Leave it to me, I assure you是“交给我吧，你尽管放心”的意思，是一种承诺；I'm afraid I can't make it by then是对邀请的婉言谢绝。