Singular and Plural.
I Have a child; I have two children.
I can play the piano.
They can visit us.
She can come tonight.
I could sing.
I could love you.
They could help me.
You must wait for me.
I must eat everything.
You must study to pass the exam.
Today I have to train.
I have to eat a piece of fruit everyday.
Oh my Good!!! Tomorrow I have to work.
You should get up.
They should be arriving at any moment.
I should go out tonight with my friends.