A binary star is actually a pair of stars that are held together by the force of gravity. Although occasionally the individual stars that compose a binary star can be distinguished, they generally appear as one star. The gravitational pull between the individual stars of a binary star causes one to orbit around the other. From the orbital pattern of a binary, the mass of its stars can be determined: the gravitational pull of a star is in direct proportion to its mass, and the strength of the gravitational force of one star on another determines the orbital pattern of the binary.Scientists have discovered stars that seem to orbit around an empty space. It has been suggested that such a star and the empty space rally composed a binary star. The empty space is known as a “black hole,” a star with such strong gravitational force that no light is able to get through. Although the existence of black holes has not been proven, the theory of their existence has been around for about two centuries, since the french mathematician Pierre Simon the leplace first proposed the concept at the end of the eighteenth century. Scientific interest in this theory has been intense in the last few decades. However, currently the theory is unproven. Black holes can only be potentially identified based on the interactions of objects around them, as happens when a potential black hole is part of a binary star; they, of course, cannot be seen because of the inability of any light to escape the star’s powerful gravity.

12. A binary star could best be described as ....................
answer choices
(A) Star that have been forced apart
(B) A star with a strong gravitational force
(C) Two star pulled together by gravity
(D) A large number of attached stars

13. The word “distinguished” in paragraph 1 is closest in meaning to .....................
answer choices
(A) Renowned
(B) Tied
(C) Celebrated
(D) Differentiated

14. According to the passage, what happens as a result of the gravitational force between the stars?
answer choices
(A) One star circles the other.
(B) The mass of the binary star increases.
(C) A black hole is destroyed.
(D) The gravitational force decreases.

15. The word “proportion” in paragraph 1 is closest in meaning to which of the following?
answer choices
(A) Contrast
(B) Ratio
(C) Inversion

(D) Force-

16. A “black hole” in paragraph 2 is ................
answer choices
(A) An empty space around which nothing orbits
(B) A star with close to zero gravity
(C) A star whose gravitational force blocks the passage of light
(D) An empty space so far away that no light can reach it
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17. Which of the following statements about black holes is NOT supported by the passage?
answer choices
(A) A black hole can have a star orbiting around it.
(B) A binary star can be composed of a black hole and a visible star.
(C) All empty space contains black hole.
(D) The gravitational pull of a black hole is strong.
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18. The word “get” in paragraph 2 could best be replaced by ................
answer choices
(A) Pass
(B) Sink
(C) Jump
(D) See
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19. Which of the following is implied in the passage about the theory of black holes?
answer choices
(A) No reputable scientists believe it.
(B) It has only recently been hypothesized.
(C) At least some scientists find it credible.
(D) Scientists are hoping to see a black hole in order to prove the theory.
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20. The word “intense” in paragraph 2 is closest in meaning to ...........................
answer choices
(A) Brilliant
(B) Intermittent
(C) Bright
(D) Strong
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21. This passage would probably be assigned reading in a course on ........................
answer choices
(A) Botany
(B) Astrophysics
(C) Geology
(D) Astrology