Imagine that you are writing an e-mail to a government official to ask him or her to provide information to your town about how to conserve water. Which sentence uses an appropriate tone for an e-mail to a government official? So we were thinking you could give us all the best tips.
You would be the coolest if you taught us how not to waste water.
It would benefit many people to learn how to help protect our environment.
I’m not sure how much you know about conserving water, but I bet it’s a lot.

The answer would be "It would benefit many people to learn how to help protect our environment."

Explanation:

This sentence uses proper words such as "Benefit" and "Environment" its also short and simple all the while keeping an appropriate air of importance, this will allow the reader to understand what the letter is about and prepare accordingly.

It would benefit many people to learn how to help protect out environment.

Explanation:

all of the other sentences are not formal, if you were talking to a person with a high rank than you would want to address them formally.