1.
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.（helpful in doing sth&helpful for sb to do sth均可）

(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

(E) that shoots dead chickens at airplanes has proved helpful in demonstrating

D为什么不对呢？觉得应该是proves itself helpful 啊，再者为什么要用完成时态呢？