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

     The most thoroughly studied cases of deception strategies employed by ground-nesting birds involve plovers, small birds that typically nest on beaches or in open fields, their nests merely scrape in the sand or earth. Plovers also have an effective repertoire of tricks for distracting potential nest predators from their exposed and defenseless eggs or chicks.

     The ever-watchful plover can detect a possible threat at a considerable distance. When she does, the nesting bird moves inconspicuously off the nest to a spot well away from eggs or chicks. At this point, she may use one of several ploys. One technique involves first moving quietly toward an approaching animal and then setting off noisily through the grass or brush in a low, crouching run away from the nest, while emitting rodent like squeaks. The effect mimics a scurrying mouse or vole, and the behaviour rivets the attention of the type of predators that would also be interested in eggs and chicks.

     Another deception begins with quiet movement to an exposed and visible location well away from the nest. Once there, the bird pretends to incubate a brood. When the predator approaches, the parent flees, leaving the false nest to be searched. The direction in which the plover "escapes" is such that if the predator chooses to follow, it will be led still further away from the true nest.

     The plover's most famous stratagem is the broken-wing display, actually a continuum of injury-mimicking behaviours spanning the range from slight disability to near-complete helplessness. One or both wings are held in an abnormal position, suggesting injury. The bird appears to be attempting to escape along an irregular route that indicates panic. In the most extreme version of the display, the bird flaps one wing in an apparent attempt to take to the air, flops over helplessly, struggles back to its feet, runs away a short distance, seemingly attempts once more to take off, flops over again as the "useless" wing fails to provide any lift, and so on. Few predators fail to pursue such obviously vulnerable prey.

     Needless to say, each short run between "flight attempts" is directed away from the nest.

What does the passage mainly discuss?