精品一区二区免费在线观看_国产精品久久久久久av福利软件_97成人精品区在线播放_国内成人精品一区

Can people change their skin color without suffering like pop king Michael Jackson? Perhaps yes.Scientists have found the gene that determines skin color.

　 The gene comes in two versions, one of which is found in 99 per cent of Europeans.The other is found in 93 t0 100 per cent of Africans, researchers at Pennsylvania State University report in the latest issue of Science.

Scientists have changed the color of a dark - striped zebrafish(斑馬魚) to uniform gold by inserting a version of the pigment(色素) gene into a young fish.As with humans, zebrafish skin color is deter-mined by pigment cells，which contain melanin(黑色素).The number, size and darkness of melanin perpigment cell determine skin color.

It appears that, like the golden zebrafish, light - skinned Europeans also have a mutation (變異) in the gene for melanin production.This results in less pigrnented skin.

　 However, Keith Cheng, leader of the research team, points out that the mutation is different in hu-man ancl zebrafish genes.

　 Humans acquired dark skin in Africa about l.5 million years ago to protect bodies from ultra - violetrays of the sun. which can cause skin cancer.

But when modem humans leave Africa to live in northem latitudes, they need more sunlight on their skin to produce vitamin D. So the related gene changes, according to Cheng.

Asians have the same version of the gene as Africans, so they probably acquired their light skin through the action of some other gene that affects skin color, said Cheng.

The new discovery could lead to medical treatments for skin cancer.lt also could lead to research in-to ways to change skin color without damaging it like chemical treatment did on Michael Jackson.

56.Scientists have done an experiment on a dark -striped zebrafish in order to

A.fincl the different genes o humans'

B.prove the humans' skin color is determined by the pigment gene

C.find out the reason why the Africans' skin color is dark

D.fincl out the ways of changing people's skin color

57.lt can be inferred from the passage that　　　 .

A.nowadays people who want to change their skin color have to suffer 8 lot from the damage caused by the chemical treatment

B.Europeans and Africans have the same gene

C.the new discovery could help to find medical treatments for skin cancer

D.there are two kinds of genes

58.The passage mainly tells us that　　　 .

A.scientists have found out that people's skin color is determined by the gene

B.the new discovery could lead to research into ways to change skin color safely

C. pop king Michael Jackson often changed his skin color as he liked

D.people can not change their skin color without any pain

59.The reason why Europeans are light - skinned is probably that　　　 .

A.they are bom light - skinned people

B.light - skinned Europeans have mutation in the gene for melanin production

C. th　　　 ey have fewer activities outside

D.they pay much attention to protecting their skin

60.The writer's attitude towarcls the discovery is　　　 .

A.neutral　　　　　　　 B.negative　　　　　　　　　　 C.indifferent　　　　 D.positive

The Coalition for the Homeless is an organization that seeks to address the needs of the homeless population in the United States. It is a network of offices, some of which provide food and houses for the homeless population, and some of which fight for the passing of laws that would give every American the right to a place to call home. According to the Coalition’s studies, of over two hundred million people living in th U?ited States, up to three million are homeless—and the number is still growing. Since the late 1970s, fast-rising house prices, large cuts in government supported housing programs, and economic recession(經(jīng)濟衰退) have made it impossible for many Americans to meet housing costs. Sadly, this has resulted in a number of persons being forced to leave their homes and/or unable to find new affordable homes.According to another research, families with children appear to be the fastest-growing part of the homeless population, making up 39% of it. The old idea of a homeless person, that of the single man who gets drunk all the time, is no longer true. A much larger part of the population now finds itself homeless. Even worse, once a person becomes homeless, he often finds it impossible to find a job, since most employers require anyone who wants a job from them to provide a home address on a job application.

1. The word “address” in the first line probably means 　　　　 .

A. talk about　　　 B. deal with　　　 C. fight for　　　 D. write to

2. How many people are homeless in the U.S. according to the Coalition studies?

A. 39% of the population.　　　　　　　　 B. 200 million people.

C. About 3 million people.　　　　　　　　 D. About one-fifth of the population.

3. Homeless people often have difficulty finding a job because________.

A. they have no home addresses

B. they mostly have a drinking problem

C. they aren't supported by government programs

D. they often don't have enough work experience

4. What is the main cause of the rising number of the homeless in the U.S.?

A. The passing of new housing laws.

B. The fast growth of family size.　　　　　　　　　　　　　　

C. The slow construction of houses.

D. The ever-rising price of housing.