Câu hỏi:

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

The response of most animals when suddenly faced with a predator is to flee. Natural  selection has acted in a variety of ways in different species to enhance the efficacy of the behaviors, known as "flight behaviors" or escape behaviors that are used by prey in fleeing predators. Perhaps the most direct adaptation is enhanced light speed and agility.

Adaptations for speed, however, are likely to require sacrifices biter attributes, so we might expect only some species to adopt a simple fast flight strategy. Another way of enhancing the effectiveness of flight is to move in an erratic and unpredictable way. Many species, like ptarmigans, snipes, and various antelopes and gazelles, flee from predators in a characteristic zigzag fashion. Rapid unexpected changes in flight direction make it difficult for a predator to track prey.  In some species, like the European hare, erratic zigzag flight might be more effective in the  presence of predators that are faster than they are and straight flight more effective against predators that are slower. One observation that supports this suggestion is the recorded tendency for slow-flying black-beaded gulls, which are normally able to escape predators by means of direct flight, to show frequent changes in flight direction when they spot a peregrine falcon (peregrines are adept at capturing flying birds).

A quite different way of enhancing escape by flight is to use so-called "flash" behavior. Here, the alarmed prey flees for a short distance and then "freezes." Some predators are unexcited by immobile prey, and a startling flash of activity followed by immobility may confuse them. "Flash" behavior is used in particular by frogs and orthopteran insects, which make conspicuous jumps and then sit immobile. In some species, "flash" behavior is enhanced by the display of bright body markings. Good examples of insects with colorful markings are the red and yellow underwing moths. At rest, both species are a cryptic brown color. When they fly, however, brightly colored hind wings are exposed, which render the moths highly conspicuous. Similarly, some frogs and lizards have brightly colored patches or frills that may serve a “flash" function when they move quickly. Some species even appear to possess "flash" sounds. The loud buzzing and clicking noises made by some grasshoppers when they jump may serve to emphasize the movement

It can be inferred that black-beaded gulls change direction when they spot a peregrine falcon for which of the following reasons?