16. How do scientists predict the appearance of comets?
a. Calculating the orbital period of a certain comet.
b. There's no way of predicting the appearance of comets.
c. Closest approach of every comet on earth is every after 100,000 years.
d. Both a and c are used as bases for predicting the appearance of comets.

17. Why does meteor shower occur?
a. The Earth is following comets ahead of it.
b. A comet with its fragments comes close to the earth.
c. Comets enter the earth's atmosphere at the same time.
d. Earth orbiting the sun passes near the orbit of comet with its fragments.

18. When does a space rock burn up?
a. When it is outside the earth's atmosphere.
b. When it enters the earth's atmosphere.
c. Once it landed on earth.
d. Once an impact crater is formed.

19. Why is it hard to see an asteroid?
1. Because it reflects little light.
11. Because it is always on the move.
IlI. Because it doesn't move.
V. Because it reflects a lot of light.
b. ll only
c.land 11
d. IV only
a. I and I

20. Which of the following is TRUE for comets, meteors and asteroids?
a. They are fragments of large asteroid.
b. They have elliptical orbit around the Sun.
c. They are remnants of the formation of Solar System.
d. They are made up of ice and dust.​