请认真阅读下面各题，从题中所给的A、B、C、D四个选项中，选出最佳选项，并在答题卡上将该项涂黑。
21. Everybody has responsibility to save water, if future generations are to enjoy similar standard of living to the one we enjoy now.
A. the; / B. a; a C. /; the D. a; the
22. It is said that about 60% of housewives have a brand before entering the store.
A. in mind B. on sale C. in possession D. on purpose
23. — I hate school; it’s not for me. I think I’ll quit.
— You stupid! It takes effort now, but later you will benefit from it.
A. will be B. are being C. have been D. were being
24. Only if you sleep, which is equal to turning the TV set off, kept away from the unending cry of “You Need It! Buy It Now!”
A. you are B. ought you to be C. you will be D. can you be
