71.　　 D. you’d=you had

70.　　 B. be busy doing…，忙于……。

69.　　 A. sell out，“卖完”

68.　　 D. quite a nice student = a very nice student

67.　　 A. “中国的人口是多少？”相当于：How many people are there in China.

66.　　 C. borrow为非延续性动词，不能与how long连用。

65.　　 A.

64.　　 C. great changes为复数。In the last few years与完成时连用。

63.　　 A.

62.　　 B. so far，“到目前为止”，常用于完成时态。