Read the passage and choose the best answer from the four options marked A, B, C or D in the following questions. Identify your answer by writing the corresponding letter A, B, C or D on your answer sheet. (1 pts)
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 keep warm at night and conserve precious food reserves. One way to do this is to find a sheltered roost. Solitary roosters shelter in 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 do. Body contact reduces the surface area exposed to the cold air, so the birds keep each other warm. Two kinglets huddling together were found to 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 forage over a very large area. When they return in the evening some will have fed well, but others may have found little to eat. Some investigators have observed that when the birds set out 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 hunts alone, but the lesser kestrel roosts and hunts in flocks, possibly so one bird can learn from others where to 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 give the alarm. But this increased protection is partially counteracted by the fact that mass roosts attract predators and are especially 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 catch small birds perching at the margins of the roost.
What does the passage mainly discuss?
Giải bởi Vietjack
Chọn D
The big majority of students who make well in the Cambridge Proficiency Examination have learnt to use a Good monolingual dictionary effectively. Such Dictionaries provide informations, not just about the Missings for the words but about their pronunciation and grammar as well. A student who studies how to use a dictionary effectively will be able to work independently for much of the time, and will gain considerable insight to the workings of the English language. He or she will be able to confirm to the meanings for the words in a text where contextual clues are insufficient, pronounce words accurately by studying the phonological transcriptions, And use words accurately both when speaking and Writing. Make sure you make the room for at least one Good monolingual dictionary on your bookshelf- and then make sure you use it at a regular basis!
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The English term café, borrowed from French, is ultimately a ………………….of the Turkish kahve, meaning coffee. ( DERIVE )
