Natural selection is the process by which one type of animal within a species develops well because of certain characteristics that make it more likely to live than others in its group. The history of the peppered moth (桦尺蛾) is an example of the natural selection process.

In nineteenth-century England, certain types of peppered moths were able to better blend (融合) into their surroundings. During that time period, great changes were happening in Great Britain. The Industrial Revolution was part of this change, and with it came air pollution. Natural selection usually takes hundreds or even thousands of years to occur. For the peppered moth, this process occurred comparatively quickly.

At the beginning of the Industrial Age, most peppered moths in England were light-colored and covered with black markings, although a few moths had dark-colored wings. Because the light-colored moths blended into the light-colored bark on the trees, they could not be easily seen by birds that would eat them. As the air grew more polluted, however, tree trunks became covered with soot (煤烟) and became darker. The light-colored moths became easy for birds to see against the dark tree trunks. Since the dark-colored moths now had the advantage, their numbers grew. Within 50 years, the peppered moth went from being mostly light-colored to being mostly dark-colored.

In the twentieth century, the air cleared up, and the peppered moth population changed again. As tree trunks lightened due to less soot in the air, light-colored moths once again had an advantage. Their numbers increased as soot levels declined. Depending on their environment, the coloration of the moths helped them to be “naturally selected” to survive.

【小题1】What was unusual about the peppered moth’s natural selection process?

A．Its frequency.	B．Its complexity.
C．Its contributing factors.	D．Its length of time.

【小题2】What can we learn from paragraph 3?

A．Both kinds of moths preferred dark-colored trunks.

B．Light-colored moths were more sensitive to pollution.

C．Dark-colored moths were originally easier to see on trees.

D．Different kinds of moths preferred different air conditions.

【小题3】What would most likely happen if soot darkened England’s trees again?

A．Light-colored moths would die out.

B．New species of moths would appear.

C．Dark-colored moths would rise in number again.

D．Moths would be less dependent on their surroundings.

【小题4】Which of the following does the example of moths mainly demonstrate?

A．Nothing is permanent.	B．It is the fittest that survive.
C．Keep up with the times.	D．Environmental protection is essential.