81.While nuclear weapons present grave（ ）dangers, the predominant crisis of overpopulation is with us today.

44.—— What will you buy for your mother’s birthday?—— I want to buy a（）wallet for him.

43.He is very（ ）to call me tonight. I can sense that.

42.You should take the medicine now. It will（ ）you pain in your stomach.

41.It is certain that he will（ ）his business to his only daughter when he gets old.

40.The（ ）production of engines in our factory has doubled this year.

39.While studying at U.C.L.A.,Mr.Wang（ ）his old friend, whom he has not seen for nearly twenty years.

38.There is too much noise outside. I can not（ ）my attention on my work.

37.In fact, there is no（ ）liberty in any country.

36.The thief was（ ）by the police at the railway station.

35.The scientists are trying to find out the facts to（ ）their theory.