(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， 是否没prove itself adj. to这种结构？