III:   1.b        3.a

       2.d        4.c

IV:

Part1: 1. If we plant more trees, the air will be fresher.

            2. If we use fewer cars, we will reduce pollution.

            3. If we use reusable bags, we will reduce waste.

            4. If we use recycled products, we will save money.

Part2: 1. Students in class  6A will plant some trees in the school yard tomorrow morning.

            2. I will not have a birthday party this year.

            3. My children will spend their holidayin a farm.

            4. My mother will prepare food for my birthday party next week.

            5. They will have an important test on friday.

            6. They will travel to Hanoi by air.

Part3: 1. In Viet Nam, april is the hostest month of the year.

            2. Do you think money is the most imporrant thing in the world?

            3. My father thinks Brazil has the best foootball team in the world.

            4. New York is the most exciting city in the world.

Part4: 1. How often does the Olympic Games held?

            2. What are the children playing?

            3. When did the first Olympic Games take place?

            4. How old did Pele' begin his career?