In A, there are a couple of problems that come to mind immediately; first of all, the "-ing" form of the verb here is incorrect. "that shoots..." is correct here, because it describes the cannon. "Shooting" makes it sound like the cannon is continually shooting the chickens, which doesn't make sense. Second, the phrase "helpful to" is not the right idiom; "helpful in" works here, because "helpful to" makes it sound like the cannon is helping the demonstration, not like the cannon is helpful to the officials performing the demonstration. This is a tough one to explain, but I guess an example is something like this:

"Good Samaritans are helpful to strangers." versus "Good Samaritans are helpful in establishing a charitable organization."

Hope this helps!

grockit_andrea wrote:In A, there are a couple of problems that come to mind immediately; first of all, the "-ing" form of the verb here is incorrect. "that shoots..." is correct here, because it describes the cannon. "Shooting" makes it sound like the cannon is continually shooting the chickens, which doesn't make sense. Second, the phrase "helpful to" is not the right idiom; "helpful in" works here, because "helpful to" makes it sound like the cannon is helping the demonstration, not like the cannon is helpful to the officials performing the demonstration. This is a tough one to explain, but I guess an example is something like this:

"Good Samaritans are helpful to strangers." versus "Good Samaritans are helpful in establishing a charitable organization."

Hope this helps!

Hi grockit_andrea,

How B is correct?
"has proved.." is correct as the result of the experiment is helpful even today, but by "canon shoots.." it seems as that the canon is "used to" shoot and not like this experiment was done once in past.
Please explain.