5. The word "optimal" in line 13 is closest in meaning to

　　(A) slow

　　(B) frequent

　　(C) best

　　(D) early

　　6. Which of the following is NOT mentioned as a reason that songbirds molt in the late summer?

　　(A) Fewer predators are in the woods.

　　(B) The weathers are still warm.

　　(C) The songbirds have finished breeding.

　　(D) Food is still available.

　　7. Some birds that are molting maintain balance during flight by

　　(A) constantly preening and caring for their remaining feathers

　　(B) dropping flight feathers on both sides at the same time

　　(C) adjusting the angle of their flight to compensate for lost feathers

　　(D) only losing one-third of their feathers

　　8. The word "Others" in line 21 refers to

　　(A) ducks

　　(B) sides

　　(C) species

　　(D) flight feathers

　　9. The author discusses ducks in order to provide an example of birds that

　　(A) grow replacement feathers that are very long

　　(B) shed all their wing feathers at one time

　　(C) keep their innermost feathers

　　(D) shed their outermost feathers first

　　10. It can be inferred from the discussion about ducks that the molting of their flight feathers takes

　　(A) a year

　　(B) a season

　　(C) several months

　　(D) a few weeks

　　參考答案：CABDC ABCBD