19. The word "they" in line 25 refers to
(A) a few birds
(B) mass roosts
(C) predators
(D) trees.

15. Which of the following statements about lesser and common kestrels is true? (A) The lesser kestrel and the common kestrel have similar diets. (B) The lesser kestrel feeds sociably but the common kestrel does not. (C) The common kestrel nests in larger flocks than does the lesser kestrel. (D) The common kestrel nests in trees, the lesser kestrel nests on the ground.

16. The word "counteracted" in line 24 is closest in meaning to (A) suggested (B) negated (C) measured (D) shielded

17. Which of the following is NOT mentioned in the passage as an advantage derived by birds that huddle together while sleeping? (A) Some members of the flock warm others of impending dangers. (B) Staying together provides a greater amount of heat for the whole flock. (C) Some birds in the flock function as information centers for others who are looking for food. (D) Several members of the flock care for the young.

18. Which of the following is a disadvantage of communal roosts that is mentioned in the passage? (A) Diseases easily spread among the birds. (B) Groups are more attractive to predators than individual birds. (C) Food supplies are quickly depleted (D) Some birds in the group will attack the others.

20. What does the passage mainly discuss? (A) Causes of food spoilage. (B) Commercial production of ice (C) Inventions that led to changes in the American diet. (D) Population movements in the nineteenth century.

21. The phrase "in season" in line 2 refers to (A) a kind of weather (B) a particular time of year (C) an official schedule (D) a method of flavoring food.

22. The word "prevent" in line 4 is closest in meaning to (A) estimate (B) avoid (C) correct (D) confine

23. During the 1860's, canned food products were (A) unavailable in rural areas (B) shipped in refrigerator cars (C) available in limited quantities. (D) A staple part of the American diet.

24. It can be inferred that railroad refrigerator cars came into use (A) before 1860 (B) before 1890 (C) after 1900 (D) after 1920

25. The word "them" in line 14 refers to (A) refrigerator cars (B) perishables (C) growers (D) distances