问题 选择题

如图所示,两条虚线之间的部分表示生态系统功能正常的作用范围。y表示一个外来干扰使之偏离这一范围的大小;x表示恢复到原状态所需的时间;曲线与正常范围之间所夹的面积可以作为总稳定性的定量指标(TS)。下列说法正确的是

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A.在正常作用范围内,生态系统中生物的种类和数量保持不变

B.在遭到干扰时,x、y值的大小与生物的种类有关,与数量无关

C.一般来说,对同一个生态系统,y值和x值之间呈负相关

D.TS值越小,这个生态系统的总稳定性越大

答案

答案:C

选择题
单项选择题

Most towns up to Elizabethan times were smaller than a modern village and each of them was built around its weekly market where local produce was brought for sale and the town folks sold their work to the people from the countryside and provided them with refreshment for the day. Trade was virtually confined to that one day even in a town of a thousand or so people. On market days craftsmen put up their stalls in the open air whilst on one or two other days during the week the townsman would pack up his loaves, or nails, or cloth, and set out early to do a day’s trade in the market of an adjoining town where, however, he would be charged a heavy toll for the privilege and get a less favourable spot for his stand than the local craftsmen. Another chance for him to make a sale was to the congregation gathered for Sunday morning worship. Although no trade was allowed anywhere during the hours of the service (except at annual fair times), after church there would be some trade at the church door with departing country folk.

The trade of markets was almost wholly concerned with exchanging the products of the nearby countryside and the goods sold in the market but particularly in food retail dealing was distrusted as a kind of profiteering. Even when there was enough trade being done to afford a livelihood to an enterprising man ready to buy wholesale and sell retail, town authorities were reluctant to allow it.

Yet there were plainly people who were tempted to “forestall the market” by buying goods outside it, and to “regrate” them, that is to resell them, at a higher price. The constantly repeated rules against these practices and the endlessly recurring prosecutions mentioned in the records of all the larger towns prove that some well-informed and sharp-witted people did these things.

Every town made its own laws and if it was big enough to have craft guilds, these associations would regulate the business of their members and tried to enforce a strict monopoly of their own trades. Yet while the guild leaders, as craftsmen, followed fiercely protectionist policies, at the same time, as leading townsmen, they wanted to see a big, busy market yielding a handsome revenue in various dues and tolls. Conflicts of interest led to endless, minute regulations, changeable, often inconsistent, frequently absurd. There was a time in the fourteenth century, for example, when London fishmongers were not allowed to handle any fish that had not already been exposed for sale for three days by the men who caught it.

Craftsmen might prefer to trade in their own town because()

A. there they could easily find good refreshment

B. there they could work in the open air

C. there they could start work very early

D. there they could have the well-placed stalls