17. Only when you go through the mental exercises to ________ a tentative definition should you open the dictionary to see if you are right.

　　[A]: come up to

　　[B]: come up for

　　[C]: come up with

　　[D]: come up through

　　【世博精解】：“keep up with”是“提出，想出”的意思。“come up to”的意思是“达到，赶得上”。“come up for”意为“参加(竞选)”

　　Key to exercise: C