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.

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.

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.

其他試題

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.