求助！定语从句还是分词短语呢？

According to United States Air Force official,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 helpful to demonstrate

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

the key is the use of 'helpful'

'be helpful in doing sth' is always the right one.

remember this. should be useful~

嗯，找到答案了。

谢谢楼上的。

2．Help用法

help somebody to do something,help (to do) something.helpful in doing