A: Did you go anywhere during summer vacation, Jeff?
B: Actually, I went to the Red Baron Flight School in Australia.
A: Australia? Wow! You must have taken some pretty serious aerobatic training there.
B: Yes, the flying was 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.
In North American English, you may use been or gone if you are describing the probability of an action that represents finished or completed travel. However, if the actor of the sentence is no longer present, 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 here, not on holiday now.)
Elena has a coffee. She must have been / gone to the restaurant.
(She is here, not in the restaurant now.)
Exercise
Open the exercise to begin the activity. Follow the instructions in the document.