Question 17:
If Ben finishes his homework early, he can relax and watch TV. (permission)
Ben has permission to relax and watch TV if he finishes his homework early.

Question 18:
If it rains, we ____ indoor activities instead of going outside. (possibility)
If it rains, we might do indoor activities instead of going outside.

Question 19:
If they work together on projects, they can share ideas and learn more. (ability)
If they work together on projects, they are able to share ideas and learn more.

Question 20:
If she completes her assignments, she should check her work for mistakes. (advice)
If she completes her assignments, she ought to check her work for mistakes.

Question 21:
If you want to improve your grades, you ____ all your assignments. (obligation)
If you want to improve your grades, you must complete all your assignments.