Read and choose the correct answer (A, B, C, or D) to each of the following questions.

The idea of life in outer space has been talked about for a long time. Some scientists say that life development on Earth was far too unlikely for it to have happened anywhere else. Things had to be perfect for us to make it on this planet. Other scientists say that space is too big. Stars and other planets are far too numerous for there to be no other life in the universe. For many years, there have been reports of visitors from other planets. People all around the world have claimed to see alien spaceships or even aliens themselves. There have been glimpses of these so-called UFOs (unidentified flying objects) flying through the air and they have even been captured on video. Some Americans believe that the U.S. Army found an alien spaceship crashed in the desert and then lied to the press about it. Although these sightings may be true, scientists have not found significant evidence that aliens exist.

If you go out into the countryside on a clear night and look up, you can see thousands of stars. Those stars make up a tiny part of our universe. There are more stars, planets, and galaxies than we can count. Even the smartest scientists can't even come close to defining how big space is. The number of possible stars and planets out there is bigger than our ability to count. If we are really on the only planet that can sustain life, then we are very special in a universe full of amazing things.