- 2017年12月06日14:36 来源：小站整理
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Molting is one of the most involved processes of a bird's annual life cycle. Notwithstanding
preening and constant care, the marvelously intricate structure of a bird's feather inevitably wears
out. All adult birds molt their feathers at least once a year, and upon close observation, one can
recognize the frayed, ragged appearance of feathers that are nearing the end of their useful life.
Two distinct processes are involved in molting. The first step is when the old, worn feather is
dropped, or shed. The second is when a new feather grows in its place. When each feather has
been shed and replaced, then the molt can be said to be complete. This, however, is an abstraction
that often does not happen: incomplete, overlapping, and arrested molts are quite common.
Molt requires that a bird find and process enough protein to rebuild approximately one-third of
its body weight. It is not surprising that a bird in heavy molt often seems listless and unwell. But
far from being random, molt is controlled by strong evolutionary forces that have established an
optimal time and duration. Generally, molt occurs at the time of least stress on the bird. Many
songbirds, for instance, molt in late summer, when the hard work of breeding is done but the
weather is still warm and food still plentiful. This is why the woods in late summer often seem so
quiet, when compared with the exuberant choruses of spring.
Molt of the flight feathers is the most highly organized part of the process. Some species, for
example, begin by dropping the outermost primary feathers on each side (to retain balance in the
air) and wait until the replacement feathers are about one-third grown before shedding the next
outermost, and so on. Others always start with the innermost primary feathers and work outward.
Yet other species begin in the middle and work outward on both sides. Most ducks shed their wing
feathers at once, and remain flightless for two or three weeks while the replacement feathers grow.
1. The passage mainly discusses how
(A) birds prepare for breeding
(B) bird feathers differ from species
(C) birds shed and replace their feathers
(D) birds are affected by seasonal changes
2. The word "Notwithstanding" in line 2 is closest in meaning to
(B) because of
(C) instead of
3. The word "intricate" in line 2 is closest in meaning to
4. The word "random" in line 12 is closest in meaning to
5. The word "optimal" in line 13 is closest in meaning to
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
(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