Exercise 1:

1. A serious road accident happened while we were waiting for the bus yesterday.
2. We had picked up trash before we left the campsite.
3. It started raining when they were putting up the tent.
4. After I get my parents' permission, I will go out with my friends.
5. When the weather was bad, we were on holiday last month.
6. I will call my mom as soon as I get the result.
7. When it rains, my father usually drives me to school.
8. Jack can't play games before he finishes his homework.

Exercise 2:

1. I will pick you up as soon as you get off the bus. (soon)
2. The rich girl rarely checks price tags when buying brand-name clothes.
3. While they were having their dinner, a flash flood swept through their house.
4. It was snowing heavily at 10 p.m. yesterday.
5. I will pick you up as soon as I leave the shopping mall.
6. While Emily was browsing online for items, her sister was playing the piano.
7. It took the firemen three days to put out the forest fire.
8. We should protect endangered species.
9. Too much carbon dioxide (CO2) in the atmosphere causes global warming.
10. What can we do to cut our carbon footprint?
11. Josh never eats carrots and peas.