问题 单项选择题 B1型题

我国制定的六种毒物的生物限值,其中哪项是铅的生物监测指标()。

A.尿中镉

B.尿中三氯乙酸

C.尿中甲基马尿酸

D.尿中马尿酸

E.血中铅

答案

参考答案:E

解析:1.尿中马尿酸是毒物甲苯的代谢产物。2.铅进入体内后的存在成分是血铅和尿铅,但后者的浓度受许多因素影响,有时不能准确反映机体内的剂量。血铅是毒物铅的毒物原形,因此,血铅作为优先选择的生物监测指标。3.尿中三氯乙酸是毒物三氯乙烯的代谢产物。

选择题
阅读理解

B

Most musicians agree that the best violins were first made in Italy.They were made in Cremona, Italy, about 200 years ago.These violins sound better than any others.They even sound better than violins made today.Violin makers and scientists try to make instruments like the old Italian violins.But they aren’t the same.Musicians still prefer the old ones.No one really knows why these old Italian violins are so special, but many people think they have an answer.

Some people think it is the age of the violins.They say that today’s violins will also sound wonderful someday.But there is a problem here.Not all old violins sound wonderful.Only those from Cremona are special.So age cannot be the answer.There must be something different about Cremona or those Italian violin makers.  

Other people think the secret to those violins is the wood.The wood of the violin is very important.It must be from certain kinds of trees.It must not be too young or too old.Perhaps the violin makers of Cremons knew something special about wood for violins.

But the kind of wood may not be so important.It may be more important to cut the wood in a special way.Wood for a violin must be cut very carefully.It has to be the right size and shape.The smallest difference will change the sound of the violin.Musicians sometimes think that this was the secret of the Italians.Maybe they understood more than we do about how to cut the wood.

Size and shape may not be the answer either.Scientists measured these old violins very carefully.They can make new ones that are exactly the same size and shape.But the new violins still do not sound as good as the old one.Some scientists think the secret may be the varnish, which covers the wood of the violin and makes it look shiny.It also helps the sound of the instrument.No one knows what the Italian violin makers used in their varnish.So no one can make the same varnish today.

There may never be other violins like the violins of Cremona.Their secret may be lost forever.Young musicians today hope this is not true.They need fine violins.But there aren’t very many of the old violins left.Also, the old violins are very expensive.Recently, a famous old Italian violin was sold for about US $ 300,000!

60.This passage is about _______.

   A.making violins                 B.musical   instruments

   C.scientific ideas                  D.the old Italian violins

61.The best violins _______.

A.are made with modern techniques      B.were lost   many years ago

C.were made in Italy 200 years ago      D.were made by scientists.

62.Some people think that modem violins ______.

A.will sound better in the future     B.will sound worse in the future

C.sound wonderful naturally         D.will never be as old as those from Cremona

63.Violins made today _______.

   A.look the same as the old ones

   B.sound the same as the old ones

   C.are better than the old ones   

D.have the same varnish as the old ones