[讨论]

According to United States Air Force officials, a cannon shooting dead chickens at airpanes 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 shoot dead chinckens at airplanes has proved helpful in demonstrating

答案是E,A为什么不行？

我选D。