You use energy every day. Energy is the ability (21) change. When you ride a bike, you use energy from your body to make the bike move. Your parents use heat energy to change the food (22) raw to cooked.

Not all energy is used as soon as you get it. Sometimes energy is (23) to be used later, stored energy can be chemical energy stored in a battery or in your body. It can also be potential energy. Potential energy is based on (24) position of the object. A soccer player standing ready to kick a ball has potential energy.

Energy of motion is also called kinetic energy. Potential energy converts, or changes into, kinetic energy when the thing or person begins to move. When the soccer player kicks the ball, kinetic energy is at work. Energy often changes forms. When you (25) the light, electricity converts into light. When you eat, chemical energy from your food converts into thermal and mechanical energy that allows you to move and work.

Flying cars aren’t just science fiction anymore. Terrafugia, based in the United States, is developing a readable aircraft called the Transition. The vehicle has two seats, four wheels and wings that fold up, so it can be driven like a car. Terrafugia first began to work on the Transition in 2006 and has come closer than anyone to making the flying car a reality. The company uses special tires and glass that are lighter than normal automotive ones, which makes it easier for the vehicle to fly. An owner needs to pass a test and complete 20 hours of flying time to be able to fly the Transition. The Transition can reach around 70 miles per hour (mph) on the road and 115 mph in the air. On the ground, it gets 35 miles per gallon.

Overpopulation is a real problem. It could kill the Earth. Very soon, there will be too many people and not (31) .

There won’t be enough farms to grow food for everyone. We’ll eat all of the fish in the sea. And our pollution will cause more (32) . I think we are in a very serious situation.

I don’t know what the answer is. Our leaders don’t seem too (33) . They never see the bigger picture. The world’s population is exploding, and explosions cause great damage.

More and more people are living longer and longer. We have better (34) . Our scientists have found cures to many diseases. There are many reasons. What we really need to do is to think about how overpopulation (35) the Earth.