题目

关于声现象，下列说法错误的是：A．一切正在发声的物体都在振动;             B．声音在真空中传播的速度最大;C．各种乐器音色不同因此能够区分它们;       D．道路两旁植树可有效减弱噪声的传播. 答案：BCan people change their skin colour without suffering like pop king Michael Jackson? Perhaps yes. Scientists have found the gene that determines skin colour.The gene comes in two versions, one of which is found in 99 per cent of Europeans. The other is found in 93 to 100 per cent of Africans, researchers at Pennsylvania State University report in the latest issue of Science.Scientists have changed the colour of a dark-striped zebrafish to uniform gold by inserting a version of the pigment(色素) gene into a young fish. As with humans, zebrafish skin colour is determined by pigment cells, which contain melanosomes(黑色素). The number, size and darkness of melanosomes per pigment cell determines skin colour.It appears that, like the golden zebrafish, light-skinned Europeans also have a mutation(变异) in the gene for melanosome production. This results in less pigmented skin.However, Keith Cheng, leader of the research team, points out that the mutation is different in human and zebrafish genes.Humans acquired dark skin in Africa about 1.5 million years ago to protect bodies from ultra-violet rays of the sun(太阳光紫外线), which can cause skin cancer.But when modern humans leave Africa to live in northern 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 colour, said Cheng.The new discovery could lead to medical treatments for skin cancer. It also could lead to research into ways to change skin colour without damaging it like chemical treatment did on Michael Jackson1.The passage mainly tells us that ________A.people can not change their skin colour without any painB.the new discovery could lead to search into ways to change skin colour safelyC.pop king Michael Jackson often changed his skin colour as he likedD.scientists have found out that people’s skin colour is determined by the gene2.It can be inferred from the passage that ________A.nowadays people who want to change their skin colour have to suffer a lot from the damage caused by the chemical treatmentB.Europeans and Africans have the same geneC.the new discovery could help to find medical treatments for skin cancerD.there are two kinds of genes3.Scientists have done an experiment on a dark-striped zebra fish in order to ________A.find the different genes of humans’B.prove the humans’ skin colour is determined by the pigment geneC.find out the reason why the Africans’ skin colour is darkD.find out the ways of changing peopl’s skin colour4.The reason why Europeans are light-skinned is probably that ________A.they are born light-skinned peopleB.light-skinned Europeans have mutation in the gen for melanosome productionC.they have fewer activities outsideD.they pay much attention to protecting their skin5.The writer’s attitude towards the discovery is ________A.neutralB.negativeC.positiveD.indifferent