canon

[crazy800]

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.
(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


Official Answer

SPOILER: E

[bear&bull]

there is a subtle difference between Helpful in demonstrating and helpful to demonstrate


Helpful to demonstrate is an activity that needs to be done

Helpful in demonstrating:

When the action has already been done, we stick to helpful in ..

this action might be useful for future and needs to be performed again , if necessary .

HTH!

[mitzi]

Thanks for the great explanation. bear&bull pointed!

In addition to this,

One of the key clues is whether we use 'shooting' or 'that shoots'

shooting suggests that canon is shooting now.
that shoots... modifies 'a canon' and is congruent with the tense of verb.