Most scientists believe that for another planet to have life on it, it must be similar to Earth in several ways. It is likely to need an atmosphere (air) and water. It also must orbit a star, like the Sun, at a good distance. This star would provide the right amount of light and heat for life to exist.

Scientists have studied planets and moons in our solar system to see if they can support life. Space probes have searched for traces of bacteria or other tiny living things on Mars. Some scientists are also looking for the possibility of life outside our solar system. Using radio telescopes, they hope to capture signals from intelligent aliens.

So far, no evidence of extraterrestrial life has been found. However, scientists have discovered hundreds of planets that orbit distant stars. Some of these planets are an ideal distance from their stars, and some are roughly the size of Earth. It may be possible that life has developed on one or more of them.

96. The best title for the passage could be ______.

A. "The Search for Alien Life"                                          B. "The Search for a New Planet"

C. "A Promising Planet Supporting Life"                        D. "Evidence of Life on Other Planets"

97. Most scientists believe that a life supporting planet must be ______.

A. somewhat similar to Earth                                            B. exactly the same Earth

C. in our solar systems                                                        D. at a good distance from Earth

98. The phrase "Space probes" most likely means ______.

A. "vehicles that travel in space, carrying spacecraft"

B. "spacecraft that collect information about the conditions of the Sun"

C. "vehicles that travel in space, carrying people"

D. "spacecraft without people on them that collect information about a planet"

99. The scientists use radio telescopes in order to ______.

A. search for traces of bacteria or other tiny living things

B. catch signals from creatures on other planets

C. search for planets that are an ideal distance from their suns

D. discover planets that are roughly the size of Earth

100. Which of the following is NOT true according to the passage?

A. Planets need water and air to support life.

B. If a sun is the right distance from a planet, the planet could support life.

C. Scientists have looked at the possibility of life only in our solar system.

D. Space probes capture signals from intelligent aliens.