help/helpful的用法

请问一个小问题

我听赵丽的课上讲除了help+in错，其他都可以。我就引申为helpful in也不对。

我查字典也看到helpful一般加to

今天又听到赵丽的课。这一题：

According to United
                    State 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.

   (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 helpfull 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

选E，用了helpful in doing.

请问这样用对吗？还是说E选项是最佳答案，其他的比它更错？