1.
1, started
2, play
3, had
4, is held
5, bought
6, has worked
2.
1, If we polute the air, we will have breathing broblems.
2, If people polute the water, a lot of fish will die.
3, If we cut down trees in the forest, there will be more floods.
4, If the soil is polluted, plants will die.
5, If the Earth becomes hotter, the sea level will rise.
3.
1. c
2. a
3. a
4. b
5. d
6. d
