问题 选择题

“一母生九子,连母十个样”,说明生物具有变异的现象.下列关于变异现象的说法,不准确的是(  )

A.生物的变异,既有可遗传变异,又有不可遗传变异

B.单纯由环境引起的变异,是可遗传变异

C.遗传物质发生了改变的变异,是可遗传变异

D.生物的变异是普遍存在的

答案

变异是指子代与亲代之间的差异,子代个体之间的差异的现象.按照变异对生物是否有利分为有利变异和不利变异.有利变异对生物生存是有利的,不利变异对生物生存是不利的.按照变异的原因可以分为可遗传的变异和不遗传的变异.可遗传的变异是由遗传物质改变引起的,可以遗传给后代;由环境改变引起的变异,是不遗传的变异,不能遗传给后代.因此生物的变异根据能否传给后代,而分为可遗传的变异和不可遗传的变异.可见选项B符合题意.

故选B

单项选择题
阅读理解

Dr. Jack M. Gwaltney, Jr. a professor at the University Of Virginia School Of Medicine infected six student volunteers with virus, the most common cause of colds. A few days later, when they were coughing and sneezing, he gathered 37 more people and divided them into three groups. Group 1 members spent three days and nights in the same room with one of the infected students, separated by a screen so they couldn't touch one another. Group 2 sat around a table while an infected volunteer talked, coughed and sang to them. Group 3 held hands with an infected student for ten seconds, and then touched their own noses or eyes.

Although most scientists at the time, the mid-70s, believed colds were spread by virus-laden droplets spread through the air when infected people coughed or sneezed, Gwaltney suspected physical contact might play an important role. Sure enough, of the 15 people who had touched a student volunteer, 11 became infected—compared with only one of those who had been sitting at the table, and none who had spent three days and nights together.

"The best evidence we have is that hand-to-hand contact is the most efficient way of transmitting virus," says Gwaltney. The study was one of a series that helped establish Gwaltney's reputation as a leading authority. Dr. Robert Couch says, "It would not be inappropriate to call him Mr. Common Cold."

When Gwaltney is asked how close scientists are to finding a cure, he replies: "If you mean ‘get rid of’, I don't think we're going to be able to do that with cold viruses any time soon. But if you look in the dictionary, you'll see that 'cure' is explained as a successful treatment. And we're not just getting more effective at treating the symptoms (症状)—we're getting at the root cause too. "

小题1:Dr. Jack M. Gwaltney conducted the experiment in order to__________.

A.find out the most common cause of colds

B.infect the student volunteer

C.find out the role physical contact plays in the common colds

D.find out the role virus-laden air plays in the infection of colds小题2:The result of the experiment shows that ___ plays an important role in the infection of colds.

A.sneezing at the infected person

B.touching the infected person

C.sitting together with the infected person

D.talking with the infected person小题3:Which of the following statements is TRUE according to the passage?

A.Dr. Gwaltney was sure that hand-to-hand touch is the cause of the common cold.

B.Only one of the people who had spent three days and nights together became infected.

C.Dr. Gwaltney conducted many an experiment as to the cause of colds.

D.Dr. Gwaltney tested altogether 43 volunteers to see how they could develop colds.小题4:Mr. Common Cold is______.

A.a newly-found virus

B.a nickname (绰号) of respect to Dr. Gwaltney

C.a method to cure colds

D.a way by which the other scientists laughed at Dr. Gwaltney小题5:When Dr. Gwaltney gives a reply in the end of the passage, he means that______.

A.they have found the fundamental cause of colds

B.they have managed to wipe out the cold viruses

C.they have meant to experiment more

D.they have made much progress in dealing with colds