41. While play is important at all levels of human development， _________ takes on particular significance when children are five and six years old.
A. it
B. and
C. which
D. because it
答案：A
分析：缺主语。it 在这里作为形式主语。
参考译文：比赛对各个层次人的发展都是重要的，尤其是当小孩5、6岁大的时候，意义重大。
42. During the second and third years of life， children gain _________ over their bodies.
A. control increasing
B. increasing to control
C. control is increasing
D. increasing control
答案：D
分析：缺宾语，而且应该是 adj.修饰名词，只能选D.
参考译文：在生长的第二第三年，小孩们对自己的身体控制能力增强了。
43. All brass instruments use a mouthpiece _________ into a long cone-shaped tube.
A. is inserted
B. that inserted
C. that is inserted
D. and inserted
答案：C
分析：that引导一个定语从句，mouthpiece为先行词。A 出现两个谓语动词，错；B，D应该用被动；
参考译文：所有的铜管乐器都用一个放在长锥筒形管里的吹嘴。

45. By the mid-twentieth century， United States presidential staffs， _________ had numbered fewer than ten a century earlier， numbered in the hundreds.
A. as
B. that they
C. which
D. and
答案：C
分析：非限制性定语从句，只有which能引导非限制性定语从句
参考译文：到20时间中期，美国的总统部官员达到了几百个，而在一个世纪前，还屈指可数呢。
46. In 1966 only 60 percent of all five year olds in the United States attended kindergarten， _________ in 1985 almost 82 percent did so.
A. with
B. which
C. whether
D. while
答案：D
分析：整个句子中出现了两个谓语，缺连接词。
参考译文：在1966年，所有5岁的小孩中只有60％的参加了幼儿园，而到1985，几乎有82％的小孩上幼儿园了。
47. _________ industries， inventions， and communal endeavors of the Shakers， the best known is their fine furniture.
A. Of the many
B. Their many
C. Are the many
D. Many of the
答案：A
分析：倒装结构。当prep短语位于句首，且谓语动词为系动词时，则引起倒装。
参考译文：在基督震荡教徒所参与很多工业、发明创造和社区建设中，最闻名的是他们做的优质家具了。
48. Most fishes and many reptiles have ribs along most of the spine， but in mammals _________ only in the chest area.
A. they are found
B. finding them
C. in which they are found
D. are found
答案：A
分析：缺主语和谓语。该句不是定语从句。
参考译文：大多数鱼类和很多爬行动物沿着大部分脊柱都长有肋骨，但哺乳动物的肋骨只长在胸部位置。
49. Although the habitat of the American beech tree is now confined to the eastern United States and southeastern Canada， _________ extended as far west as California.
A. where it once
B. once
C. it once
D. and once
答案：C
分析：缺主语。A，D中的where， and 多余。
参考译文：尽管美国山毛榉树的生长地现在只限制在美东和加拿大东南部的狭窄地带，它曾经都延伸向西生长远到加州的地方。
50. Most of North America receives _________ some form of continuous plant cover except in the arid and semiarid Southwest.
A. moisture to sustain sufficient
B. sufficient moisture to sustain
C. to sustain sufficient moisture
D. sufficient to sustain moisture
答案：B
分析：缺宾语。其中形容词修饰名词，不定式表“目的”。A，C，D语序混乱。
参考译文：除了干旱和半干旱的西南地区，大部分北美地区通过吸收充足的潮湿而保持一些连续植被的形式。