6. Water is actually quite simple, but the way how the water molecule is formed gives water its unique properties.

5. He can’t speak German without make mistakes.

4. How can we rise the temperature by one degree centigrade?

3. Water, which seems so simple and common, is which makes life possible.

2. Nothing is so precious as a drop of rain.

1. Ninety-nine percent of the living space on earth are in the oceans.

25. Children under 12 years of age in that country ______ be under adult supervision when in a public library.　　 A. must　　　　　 B. may　　　　 C. can　　　　　 D. need

24. My English-Chinese dictionary has disappeared. Who ______ have taken it?

　 A. should　　　　 B. must　　　　　 C. could　　　　　 D. would

23. It has been announced that candidates ______ remain in their seats until all the papers have been collected.　　 A. can　　　　　 B. will　　　　　 C. may　　　　 D. shall

22. –Is John coming by train?　 --He should, but he ______ not. He likes driving his car.

　 A. must　　　　　 B. can　　　　　　 C. need　　　　　 D. may