Sentence 7: Unless the injured driver is very seriously hurt, it isn't necessary to prove which driver was at fault.

If you rewrote sentence 7 beginning with: It is necessary to prove which driver was at fault .....
the next words should be

1. only if the injured
2. unless the injured
3. and the injured
4. but the injured
5. so the injured

1 ?

Yes, 1.

thanks Sue almost done 2 pages left ;-)

If you rewrote sentence 7 beginning with "It is necessary to prove which driver was at fault," the next words should be "only if the injured." Therefore, the answer is option 1.