15. What is the most massive star known so far?
    (a) Altair
    (b) Proxima Centauri
    (c) Sun
    (d) Eta Carinae
Ans: (d)
16. The smallest star in the universe known so far is ____.
    (a) Gliese 623b
    (b) Proxima Centauri
    (c) Sirius
    (d) None of the above
Ans: (a)
17. A place in space where gravity pulls so much that even light cannot get out is called as _____.
    (a) dark hole
    (b) blue hole
    (c) black hole
    (d) green hole
Ans: (c)
18. How many planets are there in the solar system?
    (a) Seven
    (b) Eight
    (c) Nine
    (d) Ten
Ans: (b)
19. What is approximate age of our solar system?
    (a) 3.6 billion years
    (b) 4.6 billion years
    (c) 5.6 billion years
    (d) 6.6 billion years
Ans: (b)
20. Which of the following is the nearest star to the solar system?
    (a) Alpha Centauri
    (b) Proxima Centauri
    (c) Eta Carinae
    (d) Altair
Ans: (b)
21. The number of star(s) in our solar system is _____.
    (a) 1
    (b) 2
    (c) 3
    (d) 4
Ans: (a)