问题 选择题

在某细胞培养液中加入32P标记的磷酸分子,短时间内分离出细胞中的ATP,发现其含量变化不大,但部分ATP的末端磷酸基团已带上放射性标记,该现象能够说明的是

①ATP中远离腺苷的磷酸基团容易脱离 ②32P标记的ATP是新合成的 ③ATP是细胞内的直接能源物质 ④该过程中ATP既有合成又有分解[ ]

A.①②③④

B.①②④

C.①②③

D.②③④

答案

答案:B

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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.

In medieval markets there was little retail trade because()

A. money was never used in sales

B. producers sold directly to consumers

C. there was not enough trade being done

D. town authorities were unwilling to make a profit