"I _______ go to Australia next year." [I am not sure yet if I will go]
might
should
need to
could
"I _______ have forgotten to take my keys when I left home." [That has to be the reason I don't have my keys with me.]
can
need to
must
should
"You _______ have bought me a birthday gift." [You didn't have to]
couldn't
mustn't
shouldn't
needn't
"You're telling me a dog ate your homework? You _______ be serious!" [It is not possible that you are serious]
can't
couldn't
mustn't
wouldn't
"You _______ tell lies! Your nose will grow long if you do." [Telling lies is forbidden]
needn't
mustn't
can't
won't
"I really _______ thank you enough!" [I wish I could thank you more]
can't
wouldn't
needn't
shouldn't
"_______ we go to the movies tonight?" [What do you think of my idea?]
Will
Can
Must
Shall
"_______ we take the kids to the store with us?"[Do we have to?]
Must
Shouldn't
Can
Shall
"I _______ to go to the bathroom." [I have to go now]
could
should
must
need
"He was only joking when he remarked that you had no talent. You _______ take it so seriously!" [it is better not to take it seriously]
wouldn't
shouldn't
can't
can
"Why isn't your homework done yet? You _______ have done it yesterday." [Yesterday was the right time to do it]
should
need to
would
must
"You _______ be rude to him if you understood that he was only trying to help you." [You didn't understand him so you were rude. But if you did understand him...]
shouldn't
mustn't
wouldn't
needn't