1.During this time the selling price, and so profits, will go up and down depending on world demand.

2.Many of us believe that a person's mind becomes less active as he grows older.

3.This means that it took them longer to accomplish mental tasks than it used to.

4.For example, the older person perhaps had trouble hearing, or poor vision, or inattention, or was trying to learn the new thing at too fast a pace.

5.Not only was the shop a center of buying and selling, but also a social meeting place.

6.He will have to give advice and make decisions as problems arise, and he must know how to get his huge staff to work efficiently with their respective responsibilities.

7.Numerous studies have now shown that the overwhelming majority of colds are "caught" by hand contact.

答案：

1.在此期間，煤炭的銷售價(jià)格及其利潤(rùn)會(huì)隨著國(guó)際市場(chǎng)的需求變化而上下波動(dòng)。

2.我們很多人都認(rèn)為，一個(gè)人智力會(huì)因衰老而變得遲鈍。

3.這意味著他們完成智力活動(dòng)所需的時(shí)間比過去長(zhǎng)。

4.例如，老年人也許聽力差，眼神不好，注意力不集中，或者想盡快地學(xué)會(huì)做某一件事情。

5.過去商店不僅僅是一個(gè)買賣東西的地方，而且是一個(gè)社交場(chǎng)合。

6.他必須為手下員工出主意，問題出現(xiàn)之后要做決斷，他還必須清楚如何使自己龐大的員工隊(duì)伍各司其職，高效工作。

7.許多研究表明，絕大多數(shù)的感冒是由于手的接觸而感染的。