16. — Shall we go out for dinner tonight, Bob?

— ________.

A. You are right                                                           B. That sounds great

C. Have a nice time                                                      D. Good night

17. ________ some water and you will feel better.

A. Drink                            B. Drinking                         C. To drink                        D. If you drink

18. You will never gain success ________ you keep working hard.

A. when                             B. because                          C. if                                  D. unless