题干

在证明DNA是遗传物质的实验中,赫尔希和蔡斯分别用32P和35S标记噬菌体的DNA和蛋白质,在下图中标记元素所在部位依次是(  )

A:①④

B:②④

C:①⑤

D:③⑤

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答案(点此获取答案解析)

A

同类题4

    In the 13th century, the Italian traveler, Marco polo , traveled a long way to China , During his stay in China , he saw many wonderful things . One of the things he discovered was that the Chinese used paper money . In western countries , people did not use paper money until the 15th century . However , people in China began to use paper money in the 7th century .
    A Chinese man called CaiLun invented paper almost 2000 years ago. He made it from wood . He took the wood from trees and made it into paper . He then put these pieces of paper together and made them into a book .
     Now paper still comes from trees . We use a lot of paper every day ! If we keep on wasting so much paper , there will not be any trees on the earth . If there are no trees , there will be no paper . Every day , people throw away about 2800 tons (吨) of paper in our city . It takes 17 trees to make one ton of paper . This means that we are cutting nearly 48000 trees every day . Since it takes more than 10 years for a tree to grow , we must start using less paper now . If we don’t , we will not have enough time to grow more trees to take the place of those we use for paper .
    So how can we save paper ? We can use both sides of every piece of paper , especially when we are making notes .We can choose drinks in bottles instead of those in paper packets . We can also use cotton handkerchiefs (手帕) and not paper ones . When we go shopping , we can use fewer paper bags . If the shop assistant does give us a paper bag, we can save it and reuse it later .
    Everyone can help to save paper . If we all think carefully , we can help protect trees . But we should do it now , before it is too late .

同类题5

阅读理解

Throughout the history of the arts, thenature of creativity has remained constant to artists.Nomatter what objects they select, artists are to bring forth new forces andforms that cause change---to find poetry where no one has ever seen orexperienced it before.

Landscape (风景) isanother unchanging element of art.It can be found from ancient timesthrough the17th-century Dutch painters to the 19th-century romanticists andimpressionists.Inthe 1970s Alfred Leslie, one of the new American realists, continued thispractice.Lesliesought out the same place where ThomasCole, a romanticist, had producedpaintings of the same scene a century and a half before.UnlikeCole who insists on a feeling of loneliness and the idea of finding peace innature, Leslie paints what he actually sees.In his paintings, there is no particularchange in emotion, and he includes ordinary things like the highway in thebackground.Healso takes advantage of the latest developments of color photography to helpboth the eye and the memory when he improves his painting back in his workroom.

Besides, all art begs the age-oldquestion: What is real? Each generation of artists has shown theirunderstanding of reality in one form or another.The impressionists saw reality in briefemotional effects, the realists in everyday subjects and in forest scenes, andthe Cro-Magnon cave people in their naturalistic drawings of the animals in theancient forests.Tosum up, understanding reality is a necessary struggle for artists of allperiods.

Over thousands of years the function ofthe arts has remained relatively constant.Past or present, Eastern or Western, thearts are a basic part of our immediate experience.Many and different are the faces ofart,and together they express the basic need and hope of human beings.