British scientists have done something that，many people thought，was impossible: they created the first clone of an adult mammal（哺乳動(dòng)物）．The clone，named Dolly，is a seven-month-old sheep，grown from a cell of an adult female sheep.

    What is a clone? A clone is a copy—a genetic copy. Genes are the instructions for life. They tell a cell what to do and how to do it. Genes make each individual plant or animal different and unique. But a clone has the same genes as the original organism(生物體）．

    Cloning is not new. Plants have been cloned for centuries. New plants are often grown from cutting from another plant. Also，plants like pineapples，strawberries and carnations(康乃馨）are sometimes cloned. One benefit of cloning is that we can make many copies of the best and healthiest plants.

    It has been much more difficult to clone animals. Frogs have been cloned，but they died as tadpoles，never living long enough to become adult frogs，which made the scientists despondent. Mice，sheep and cattle have been cloned from embryos. But Dolly is the first healthy clone of an adult mammal. How did they do it?

    （1）An unfertilized egg was taken from a sheep.

    （2）The egg nucleus(細(xì)胞核）was removed.

    （3)A cell was taken from the udder(乳房）of a pregnant(懷孕的）sheep. It was“starved”，so that it stopped growing.

    （4）The two cells were combined into one，and then implanted in a third sheep，where it grew normally.

    （5）The clone was born. It was genetically identical to the pregnant sheep.

    This sounds much easier than it actually was. To end up with one clone，the scientists started with 277 udder cells. And they needed in a way to make the egg cell accept a new nucleus. They did that by starving the cell.

    It may soon be possible to clone many types of animals. Will we also be able to clone human organs，or even whole human beings? We have only begun to think about the morality of cloning technology. Maybe the question to ask is not whether we can clone humans，but instead，should we clone humans?

59. What can replace the underlined word“despondent” in the fourth paragraph?

A. calmed down          B. set down

C. cut down             D. cast down

60. Dolly is a sheep________because she is grown from a cell of an adult female sheep.

A. that has no father         B. that has no mother

C. that has no parents        D. that has no tail

61. According to the passage we can know that__________．

A. only plants can be cloned

B. only strawberries and carnations can sometimes be cloned

C. animals and plants have quite a long history of cloning

D. genes can tell a cell what to do and how to do it during cloning

62. From the fourth paragraph we can know that__________．

A. a tadpole is the early stage of a grown-up frog

B. a tadpole is a frog without a tail

C. a tadpole is a kind of animal

D. a tadpole is a clone of an adult mammal

59. 【解析】選D。詞義理解題。由第四段前兩句可推知科學(xué)家們很不高興。cast down“使沮喪；使不愉快”。

60. 【解析】選C。推理判斷題。從文中可以看出，多莉是從一只成年羊的細(xì)胞中克隆出來的，所以它沒有父母，而是那只羊的一個(gè)翻版。

61. 【解析】選D。細(xì)節(jié)理解題。D項(xiàng)“基因在克隆過程中可以告訴細(xì)胞做什么及如何去做”，文章第二段正是說的這個(gè)意思。第三段指植物可以克隆，第四段指動(dòng)物也可以克隆，所以A項(xiàng)不正確；從文中第三段可知菠蘿也是可以克隆的，所以B項(xiàng)不正確；第三段中指植物已有幾個(gè)世紀(jì)的克隆歷史，而沒有提到動(dòng)物的克隆歷史，所以C項(xiàng)與題意不符。

62.【解析】選A。推理判斷題。文章第四段第二句說：人們?cè)?jīng)克隆過青蛙，但在蝌蚪階段就死了，并沒有進(jìn)入成年青蛙階段，所以我們可以判斷，蝌蚪是青蛙的早期形態(tài)。

 

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A．Robert Edward LeeB．Robert Lee Frost
C．Ernest Hemingway D．Ezra Pound
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C．Frost was found lo have a gift in poetry while he studied in high school.
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