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
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