a) If we keep on using more and more motor vehicles, we will run out of oil.

b) If we run out of oil, we will need other kinds of energy.

c) If we use more oil and coal, pollution will increase.

d) If pollution increases, more and more trees will die.

e) If more and more trees die, the climate will change.

f) If the climate changes, we' will meet with natural disasters.

g) If we try to control pollution, it will be very expensive.