Ability
Five years ago, I (cannot, couldn't) play the piano.
Five years ago, I couldn't play the piano.
When I grow up, I (must, might) be filial.
When I grow up, I must be filial.
I think I ______ go to the beach this Sunday.
I think I might go to the beach this Sunday.
We have enough milk in the fridge so we don't have to buy some more.
don't have to - Necessity
You are asking your teacher for permission to go to the bathroom.
Could/May/Can I go to the bathroom, please?
(Can, Must) I drink a lot of water?
Must I drink a lot of water?
I am feeling tired. I ______ go to sleep now.
I am feeling tired. I should go to sleep now.
I can't help you with your homework tonight.
can't - Ability
Your friends asked you to hang out with them, but you need to study for an upcoming exam.
I must study for the upcoming exam.
The volleyball team (can not, could not) make it to the last Olympics.
The volleyball team could not make it to the last Olympics.
Carissa (has to, may) study hard to remain the top student of her school.
Carissa has to study hard to remain the top student of her school.
Naomi just lost her favorite bracelet. She ______ very sad.
must be
That can't be Megumi's sister. They don't look alike.
can't be - conclusion
You see a friend preparing a cheat sheet for the test tomorrow.
You shouldn't cheat.
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.
My mom said that I (can, have to) go to her friend's birthday party.
My mom said that I have to go to her friend's birthday party.
We are running late. We _____ hurry.
must / have to
We might go to Bali for Christmas.
might - Possibility
A friend is spreading an ugly rumor about your best friend. You don't believe it.
It can't be true. You should not spread rumors.
I (can, could) help you learn math if you study hard.
I can help you learn math if you study hard.
Billy and I (must, had to) cook dinner last night.
Billy and I had to cook dinner last night.
"We will be okay being home on our own this weekend. You ______ worry about us, Mom", said Eric, Edwin, and Edward.
don't have to
He will be having lessons for another two hours. We should visit him later.
should - Advice
You were getting ready to meet your friends at the cinema. Your car wouldn't start.
I might be late. / I may not be able to make it.