Ability
Obligation
Possibility
Permission/Requests
100
Five years ago, I (cannot, couldn't) play the piano.
Five years ago, I couldn't play the piano.
100
When I grow up, I (may, might) become an engineer.
When I grow up, I may become an engineer.
100

Charles is competing in a soccer tournament. I (can, will, may) go see him his first game.

Charles is competing in a soccer tournament. I may go see his first game.

100

Which sentence expresses permission:

1. You can go to the football game tomorrow.

2. You must go to the football game tomorrow.

You can go to the football game tomorrow. 

200
We (can, could) speak English well.
We can speak English well.
200
(Might, May) I have a glass of water?
May I have a glass of water?
300
The volleyball team (can, could) go to the Olympics this year if they are lucky.
The volleyball team could go to the Olympics this year if they are lucky.
300
There is a small chance that we (may, might) go to the beach this weekend.
There is a small chance that we might go to the beach this weekend.
400
I (cannot, couldn't) run that fast when I was six years old.
I couldn't run that fast when I was six years old.
400
If you leave the stove on, the house (may, might) catch on fire.
If you leave the stove on, the house might catch on fire.
500
I think I (can, could) help you learn math if you study hard.
I think I can help you learn math if you study hard.
500
Billy and I (may, might) cook dinner tonight.
Billy and I may cook dinner tonight.