15000 bài tập tách từ đề thi thử môn Tiếng Anh có đáp án (Phần 64)

Anthropologists have pieced together the little they know about the history of left - handedness and right - handedness from indirect evidence. Though early men and women did not leave written records, they did leave tools, bones, and pictures. Stone Age hand axes and hatchets were made from stones that were carefully chipped away to form sharp cutting edges. In some, the pattern of chipping shows that these tools and weapons were made by right handed people, designed to fit comfortably into a right hand. Other Stone Age implements were made by or for left-handers Prehistoric pictures, painted on the walls of caves, provide further clues to the handedness of ancient people. A right - hander finds it easier to draw faces of people and animals facing toward the left, whereas a left - hander finds it easier to draw faces facing toward the right. Both kinds of faces have been found in ancient painting. On the whole, the evidence seems to indicate that prehistoric people were either ambidextrous or about equally likely to be left - or right - handed.

      But, in the Bronze Age, the picture changed. The tools and weapons found from that period are mostly made for right - handed use. The predominance of right - handedness among humans today had apparently already been established.

 Insects’ lives are very short and they have many enemies, but they must survive long enough to breed and perpetuate their kind. The less insect-like they look, the better their chance of survival. To look "inedible" by resembling or imitating plants is a deception widely practiced by insects. Mammals rarely use this type of camouflage, but many fish and invertebrates do.

     The stick caterpillar is well named. It is hardly distinguishable from a brown or green twig. This caterpillar is quite common and can be found almost anywhere in North America. It is also called "measuring worm" or "inchworm." It walks by arching its body, then stretching out and grasping the branch with its front feet then looping its body again to bring the hind feet forward. When danger threatens, the stick caterpillar stretches its body away from the branch at an angle and remains rigid and still, like a twig, until the danger has passed.

Walking sticks, or stick insects, do not have to assume a rigid, twig-like pose to find protection; they look like inedible twigs in any position. There are many kinds of walking sticks, ranging in size from the few inches of the North American variety to some tropical species that may be over a foot long. When at rest their front legs are stretched out, heightening their camouflage. Some of the tropical species are adorned with spines or ridges, imitating the thorny bushes or trees in which they live.

     Leaves also seem to be a favorite object for insects to imitate. Many butterflies can suddenly disappear from view by folding their wings and sitting quietly among the foliage that they resemble.

Homing pigeons are placed in a training program from about the time they are twenty-eight days of age. They are taught to enter the loft through a trap and to exercise above and around the loft, and gradually they are taken away for short distances in wicker baskets and released. They are then expected to find their way home in the shortest possible time.

In their training flights or in actual races, the birds are taken to prearranged distant points and released to find their way back to their own lofts. Once the birds are liberated, their owners, who are standing by at the home lofts, anxiously watch the sky for the return of their entries. Since time is of the essence, the speed with which the birds can be induced to enter the loft trap may make the difference between gaining a win or a second place.

The head of a homing pigeon is comparatively small, but its brain is one quarter larger than that of the ordinary pigeon. The homing pigeon is very intelligent and will persevere to the point of stubbornness some have been known to fly a hundred miles off course to avoid a storm.

Some homing pigeon experts claim that this bird is gifted with a form of built-in radar that helps it find its own loft after hours of flight, for hidden under the head feathers are two very sensitive ears, while the sharp, prominent eyes can see great distances in daytime.

Why do homing pigeons fly home? They are not unique in this inherent skill: it is found in most migratory birds, in bees, ants, toads, and even turtles, which have been known to travel hundreds of miles to return to their homes. But in the animal world, the homing pigeon alone can be trusted with its freedom and trained to carry out the missions that people demand.