4. Fossil fuels such as coal or oil are burned. Acid gases are produced. (so)

-.

5. Eating too much sugar can result in health problem. (lead to)

- ……………………………………………………………………………………………………………..

6. David had gone home before we arrived.

- After …………………………………………………………………………………………………….

7. We had lunch then we took a look around the shops.

- Before ………………………………………………………………………………………….……

8. The light had gone out before we got out of the office.

- When………………………………………………………………………………………………….

9. After she had explained everything clearly, we started our work.

- By the time …………………………………………………………………………………………..….

10. My father had watered all the plants in the garden by the time my mother came home.

- Before ………………………………………………………………………………………….…………

11. Unless we use less fossil fuel, they will be run out soon.

If ............................................................................................................................................................

12. Unless it stops raining today, we may be faced with a serious flood.

If ...............................................................................................................................................................