55. According to United States Air Force officials, a cannon shooting dead chickens at airplanes has proved helpful to demonstrate what kind of damage can result when jets fly into a flock of large birds. (A) shooting dead chickens at airplanes has proved helpful to demonstrate (B) shooting dead chickens at airplanes has proved itself helpful as a demonstration of (C) shooting dead chickens at airplanes proves itself helpful as demonstrating (D) that shoots dead chickens at airplanes proves itself helpful to demonstrate (E) that shoots dead chickens at airplanes has proved helpful in demonstrating 答案是Ｅ 为什么用完成时呢？？？？？？？？谢谢！
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发表于 2006-3-12 21:54:00
