Answer: Students will be allowed to eat lunch on the hill outside of the cafeteria if the noise level is kept down, they stay on the hill, and trash is cleaned up afterward. If students can not be noisy, have all their trash picked up afterward, and not enter other buildings during lunch, then they can eat on the hill outside the cafeteria.
This is the strongest revision of the sentence because:
It says the students will be able to eat lunch outside on the hill, if the cafeteria noise level is kept down, they stay on the hill, and if the trash is cleaned by students.
So, it is the answer to the question.
Hope this answer helps you!