1 - if we keep on using more and more cars, we will run out of oil.
2 - if we run out of oil, we will need other kinds of energy.
3 - Pollution will increase if we use more oil and coal.
4 - if pollution increases, more and more tress will die.
5 - the climate will change if more trees die.
6 - if we try to control the pollution, it will be very expensive.
7 - if we don't control pollution soon, it will be too late.