The doctor said my headaches [could/must] _____ (be) because of the hot weather but they're going to do some tests to be sure.
could be
Do you remember my birthday party last year? You [can't/must] _____ (remember)! It was the same day as your graduation.
must remember
Have you got your passport? I'm not sure if you'll need it but they [might/must] _____ (ask) you for ID.
might ask
He [may not/can't] _____ (be) our teacher! He looks about twelve!
can't be
Take this umbrella just in case. It looks as if it [might/can] _____ (rain).
might rain
Oh no! My phone's not in my bag. I [could/must] _____ (leave) it at home.
must have left
It is still a mystery how the robber gained access to the bank. Police are investigating whether the suspect [must/may] _____ (know) one of the employees.
may have known
She [might not/can't] _____ (clean) the whole house on her own in two hours. She must have had some help.
can't have cleaned
He [could/might] not _____ (know) about it when I saw him. I'm sure he would have told me.
couldn't have known
He [mustn't/couldn't] _____ (go) to Russia. He didn't have a passport.
couldn't have gone
Come in and sit down. You [could/must] _____ (be) tired after the journey.
must be
She always gets such good grades at school. She [might/must] _____ (work) very hard.
must work
I explained the homework but she did the wrong page. She [must/might] _____ (misunderstand) me.
must have misunderstood
The exam results will be out soon. It [must/might] _____ (be) this week or possibly next week.
might be
Let's ask at reception to see if they have your keys. Someone [can/might] _____ (find) them.
might have found
Why were there no buses yesterday? Maybe it was the snow or they [might/must] _____ (be) on strike.
might have been
Your watch says a different time from mine. One of them [must/might] _____ (be) wrong.
must be
Whose is this coat? It [can't/mustn't] _____ (be) Paul's. It's way too small for him.
can't be
Who left their laptop on my desk? It [mustn't/can't] _____ (be) Mel's – she's working at home today.
can't be
You [must/may] _____ (see) her, surely! She was standing right in front of you.
must have seen
I can't remember my password! But I [may/must] _____ (write) it in my notebook as sometimes I do that.
may have written
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