"Copy the ways of nature," we were told. Yes, copy nature — for everything comes directly or indirectly from natural things. Often we have to put our knowledge to work, "treating" nature’s materials so as to make them serve our purposes better. We could, certainly, take the skin from a dead animal and at once make a pair of shoes with it; but they wouldn’t be very good shoes. For our purpose it is better first to treat the skin with chemicals that turn it into leather.
Until fairly recently our efforts to copy nature’s methods of manufacture were not very successful. Up to about 1950 only animal skins provided material for good shoes. Clothes had to be made of cotton from the cotton plant or of wool from sheep. The only kind of rubber we had came from the rubber tree. Close study of all such useful materials showed that their chemistry was simple in some ways, most complicated in others. Their basic chemicals are plentiful &mdas
A. An animal’s skin can be made into a pair of shoes for us.
B. Our purposes are not necessarily those of Nature.
C. There aren’t enough natural materials for our needs.
D. We try to copy nature — but it is difficult to do that.
"Copy the ways of nature," we were told. Yes, copy nature — for everything comes directly or indirectly from natural things. Often we have to put our knowledge to work, "treating" nature’s materials so as to make them serve our purposes better. We could, certainly, take the skin from a dead animal and at once make a pair of shoes with it; but they wouldn’t be very good shoes. For our purpose it is better first to treat the skin with chemicals that turn it into leather.
Until fairly recently our efforts to copy nature’s methods of manufacture were not very successful. Up to about 1950 only animal skins provided material for good shoes. Clothes had to be made of cotton from the cotton plant or of wool from sheep. The only kind of rubber we had came from the rubber tree. Close study of all such useful materials showed that their chemistry was simple in some ways, most complicated in others. Their basic chemicals are plentiful &mdas
A. When nature’s materials became complicated.
B. Where nature’s materials came from.
C. Why the materials were so similar to one another.
D. How she built up her materials from their parts.
The "balance of nature" is not an empty phrase. Nature provides a population to occupy a suitable environment and cuts down surplus population to fit the available food supply. One means of reducing surplus population is predators(食肉动物); others are parasites (寄生虫) and diseases. Also, population density produces nervous disorders and even drives animals to mass migrations, like the lemmings (旅鼠) of Norway who plunge into (跳入) the sea.
That predators populations increase to control other animals has long been known. Many years ago, the Hudson’s Bay Company records revealed that the fox population went up and down about a year after the rabbit population had gone up and down.
Sometimes a situation occurs in which the predators population is reduced to a level below which nature can readily replace. On Valcour Island in Lake Champlain (New York) , a costly campaign resulted in the elimination of predatory animals only to have birds and small animals&md
A. the relation of wildlife to man
B. the adequacy of the food supply to support its animal population
C. the ratio of small game to predators
D. the destruction of predators
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