1. That actress is only 20. I thought she was older.
as
That actress is not I thought.

2. Can't you type faster than that?
fastest
Is can type?

3. Mary wasn't allowed to go on holiday with her boyfriend.
let
Mary's parents didn't on holiday with her boyfriend.

4. The film started before I could get to the cinema.
had
The film when I got to the cinema.

5. We ought to start studying now.
started
It's studying.

6. You can't swim in this area.
permitted
Swimming is in this area.

7. Paul hasn't had a job for three years.
out
Paul has for three years.

8. He wrote his latest book while he was staying in Paris.
was
His latest novel stay in Paris.

9. Our fiftieth wedding anniversary is in April next year.
for
By April next year for fifty years.

10. There were a lot of cars on the road to London.
traffic
There on the road to London.