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.

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.

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

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.

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

26. The word "fixture" in line 20 is closest in meaning to (A) luxury item (B) substance (C) commonplace object (D) mechanical device

27. The author implies that in the 1920's and 1930's home deliveries of ice (A) decreased in number (B) were on an irregular schedule (C) increased in cost (D) occurred only in the summer.