Question

6 I'm sure that I lost my watch when we were on the beach.(must)
my watch when we were on the beach.
7 It only takes a little time to download a film from this website. (much)
It
time to download a film from this website.
8 I'm really sorry that I copied your work in the exam(should)
your work in the exam
9 It's possible that Tracey lied to us. (may)
to us.
Tracey
10 Every student at school came to the Open Day. (all)
at school went to the Open Day.​

Answer 1

I must have lost my watch when we were on the beach.

It doesn't take much time to download a film from this website.

I shouldn't have copied your work in the exam.

Tracey may have lied to us.

All students came to the Open Day at school.