what does the passage mainly discuss

            Birds that feed in flocks commonly retire together into roosts. The reasons for roosting             communally are not always obvious, but there are some likely benefits. In winter

            especially, it is important for birds to lớn keep warm at night and conserve precious food

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 Line     reserves. One way to lớn tự this is to lớn find a sheltered roost. Solitary roosters shelter in

  (5)      dense vegetation or enter a cavity - horned larks dig holes in the ground and

            ptarmigan burrow into snow banks - but the effect of sheltering is magnified by

            several birds huddling together in the roosts, as wrens, swifts, brown creepers,

            bluebirds, and anis tự. Body tương tác reduces the surface area exposed to lớn the cold air,

            so the birds keep each other warm. Two kinglets huddling together were found to

 (10)      reduce their heat losses by a quarter and three together saved a third of their heat.

               The second possible benefit of communal roosts is that they act as “information                          centers.” During the day, parties of birds will have spread out to lớn forage over a very

            large area. When they return in the evening some will have fed well, but others may

            have found little to lớn eat. Some investigators have observed that when the birds mix out

 (15)      again next morning, those birds that did not feed well on the previous day appear to

            follow those that did. The behavior of common and lesser kestrels may illustrate

            different feeding behaviors of similar birds with different roosting habits. The common

            kestrel hunts vertebrate animals in a small, familiar hunting ground, whereas the very

            similar lesser kestrel feeds on insects over a large area. The common kestrel roosts and

 (20)      hunts alone, but the lesser kestrel roosts and hunts in flocks, possibly sánh one bird can

            learn from others where to lớn find insect swarms.

               Finally, there is safety in numbers at communal roosts since there will always be a

            few birds awake at any given moment to lớn give the alarm. But this increased protection is

            partially counteracted by the fact that mass roosts attract predators and are especially

 (25)      vulnerable if they are on the ground. Even those in trees can be attacked by birds of

            prey. The birds on the edge are at greatest risk since predators find it easier to lớn catch

            small birds perching at the margins of the roost.

            9. What does the passage mainly discuss?

              (A) How birds find and store food

              (B) How birds maintain toàn thân heat in the winter

              (C) Why birds need to lớn establish territory

              (D) Why some species of birds nest together

            10. The word “conserve ”in line 3 is closest in meaning to

              (A) retain

              (B) watch

            (C) locate

              (D) share

            11. Ptarmigan keep warm in the winter by

              (A) huddling together on the ground with other birds

              (B) building nests in trees

              (C) burrowing into dense patches of vegetation

              (D) digging tunnels into the snow

            12. The word “magnified”in line 6 is closest in meaning to

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              (A) caused

              (B) modified

              (C) intensified

              (D) combined

            13. The author mentions kinglets in line 9 as an example of birds that

              (A) protect themselves by nesting in holes

              (B) nest with other species of birds

              (C) nest together for warmth

              (D) usually feed and nest in pairs

            14. The word “forage”in line 12  is closest in meaning to

              (A) fly

              (B) assemble

            (C) feed

            (D) rest

            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 phàn nàn 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 warn 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 lớn predators phàn nàn 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

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              (A) a few birds               (B) mass roosts

            (C) predators                   (D) trees