21. The word "Undoubtedly" in line I is closest in meaning to
(A) occasionally
(B) unexpectedly
(C) previously
(D) certainly

17. All of the following statements about the tails of comets are true EXCEPT: (A) They can contain electrically charged or neutral particles. (B) They can be formed only when there is sufficient heat. (C) They are formed before the coma expands. (D) They always point in the direction away from the Sun.

18. The word "distinct" in line 17 is closest in meaning to (A) visible (B) gaseous (C) separate (D) new

19. Compared to the tail of electrically charged atoms, the tail of neutral dust particles is relatively (A) long (B) curved (C) unpredictable (D) bright

20. What does the passage mainly discuss? (A) The effects of human activities on prehistoric wildlife (B) The origins of the hunter-gatherer way of life (C) The diets of large animals of the Pleistocene epoch (D) The change in climate at the end of the Pleistocene epoch

22. The word "components" in line 2 is closest in meaning to (A) parts (B) problems (C) changes (D) varieties

23. Which of the following is mentioned as supporting the Pleistocene overkill hypothesis? (A) Many of the animals that became extinct were quite large. (B) Humans migrated into certain regions around the time that major extinctions occurred. (C) There is evidence that new species were arriving in areas inhabited by humans. (D) Humans began to keep and care for certain animals.

24. The word "Besides" in line 13 is closest in meaning to (A) caused by (B) whereas (C) in addition to (D) in favor of

25. The author mentions saber-toothed cats in line 16 as an example of a carnivore that (A) became extinct before the Pleistocene epoch (B) was unusually large for its time (C) was not able to compete with humans (D) caused the extinction of several species

26. The word "they" in line 20 refers to (A) human hunters (B) game animals (C) other predators (D) large mammals

27. According to the passage, what is one difference between the hunting done by some humans and the hunting done by gray wolves? (A) Some humans hunt more frequently than gray wolves. (B) Gray wolves hunt in larger groups than some humans. (C) Some humans can hunt larger animals than gray wolves can hunt. (D) Some humans prey on animals of all ages, but gray wolves concentrate their efforts on young animals.