There must have been an extremely good reason for all of the dinosaurs to have suddenly become extinct about sixty-five millions years ago.
That must have been so embarrassing
His singing was so high, it must have been in falsetto.
If they really had escaped from the prison as you said, then they must have been lying when they told us they were refugees from a cruise ship's shipwreck.
It has been three hours it is time to go we must leave in about one hour
An answer to those questions has been found.
The verb in this sentence is the word "is." When you use the verb "to be," you must use the correct form of it.
It had been an amazing evening.
My prayer has been answered!
How have you been doing. This have been a beautiful day.
I have been harried to write this sentence for this student.
You must be patient and persistent.
I must cancel my doctor's appointment.