Rephrasing with a given beginning : 
You cannot go into that exclusive club if you do not wear a formal dress
Unless...............................
It would be wise for you to take a bigger car
You had........................
She felt sick because she wasn't used to flying
If.....................
I don't think the vanilla cream has enough sugar in it 
There is so.............
The man dissapeared in our car before we realised what was happening
By the time..............
I'd have to go out with you, but I have to finish this report tonight 
If................................
They are installing the new computer system in all the offices 
The new computer system..............

Răspuns :

You cannot go into that exclusive club if you do not wear a formal dress.

Unless you wear a formal dress, you cannot go into that exclusive club.

It would be wise for you to take a bigger car.

You had better take a bigger car.

She felt sick because she wasn't used to flying.
If she were used to flying, she would not feel sick.

I don't think the vanilla cream has enough sugar in it .

There is so little sugar in the vanilla cream.

The man disappeared in our car before we realised what was happening.
By the time we realized what was happening, the man disappeared in our car.

I'd have to go out with you, but I have to finish this report tonight.

If I didn't have to finish this report tonight, I would have to go out with you.

They are installing the new computer system in all the offices .

The new computer system is being installed in all the offices.