1.

If it doesn't stop raining by 11 o'clock we will cancel the picnic.

unless

We will cancel the picnic    raining by 11 o'clock.

2.

I have always played with a heavy tennis racket.

used

I    with a heavy tennis racket.

3.

Frank once enjoyed boxing, but he doesn't now.

used

Frank    boxing.

4.

I may sell my stamp collection.

thinking

I    my stamp collection.

5.

'What are you going to do tomorrow, Janet?' said Charles.

what

Charles asked Janet    to do the next day.

6.

Preparations for this party began six months ago.

getting

We    for this party for six months.

7.

The queue was so long lan couldn't get a ticket for the concert.

such

There was    lan couldn't get a ticket for the concert.

8.

I'm very tired so I don't want to go out this evening.

too

I'm    out this evening.

9.

It was the funniest film I have ever seen.

laughed

I    at a film before.

10.

I didn't invite Liz because I didn't know she liked discos.

if

I would have invited Liz    she liked discos.