A: Did you go anywhere during summer vacation, Jeff?
B: Actually, I went to Dubai.
A: Dubai? Wow! You must have seen some pretty cool cars there.
B: Yes, the cars were amazing.
The Perfect Infinitive
To use Modals of Certainty to describe the past, we use the Perfect Infinitive: Modal Verb + Have + Past Participle
John didn't come to school yesterday. He must have been sick.
It was sunny with a clear sky yesterday. It can't have rained last night.
He might have woken up late. He still hasn't arrived.
I can't contact her. She could have changed her phone number.
For the past participle of the verb, go, you may use been or gone in American English if you are describing something that is finished or completed. If you are explaining the present situation, we only use gone:
Where is Kazuko? She must have gone to the bathroom.
(She is in the bathroom now.)
I don't think Beth is at school anymore. She could have gone home.
(She is at home now.)
Wow, Sarah has a really nice tan! She must have been / gone on holiday.
(She is not on holiday now.)
Elena has a coffee. She must have been / gone to the restaurant.
(She is not in the restaurant now.)
Exercise
Open the exercise to begin the activity. Follow the instructions in the document.