3. Which of the following statements is INCORRECT?
A) The planet must be as big and heavy as the earth.
B) Proper conditions are essential to the existence of life
C) Double stars can provide steady light and heat.
D) The distance between a planet and its sun should be right.

4. What kind of planet might NOT support life?
A) Most of the planets of the stars.
B) Stars similar to our sun.
C) Planets similar to the earth.
D) Planets with proper conditions.

5. At the end of the passage the author suggests that
A) it is impossible for life to exist on planets.
B) earthlike life could only exist on a few planets.
C) life could exist on only one planet in a million.
D) life could exist on a great number of planets.