1.. If we plant more trees, the air will be fresher.
2. If the soil is polluted, the vegetables will die
3. Unless he calls me, I will stay at home.
4.The weather is not very good. It might rain this afternoon.
5.If a student recycles the papers, he will save energy.
6. I didn't clean my room for a long time.
IV.
1.is
2.in
3.the
4.of