英语题型 Plants and animals all need air .Only about one-fi

Plants and animals all need air .Only about one-fifth of the air is oxygen. The other four-fifths is another gas ,Without __41__,smell or color, named nitrogen Plants and animals need nitrogen__42__oxygen , but they cannot take it from the air __43_.how do they get __44_supply of nitrogen?

There are very small organisms in soil and water which can __45__nitogen out of the air and fix it in __46__materials which plants and animals can use .These materials are taken out by plants through their roots in water from the soil. Animals get their nitrogen __47_eating plants . __48__of this nitrogen comes away in animal waste and men have for many thousands of years __49__enough to put animal waste __50__into the soil to help plants grow .

41. A. taste B. the taste C .tastes D. the tastes

42. A. as much as B. as well as C. as many as D .as good as

43. A. themselves B. for themselves C. by them D. for them

44. A. its B. it's C .their D. theirs

45. A. send B. take C. make D. put

46. A. complicated B. raw C. chemical D. complex

47. A. with B. by C. out of D. from

48. A. some B. little C. certain D. few

49. A. knowing B. to know C .known D. know

50. A. forward B. below C .around D. back