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5、Nothing lives forever. Is that right ?Wrong. It seems hard to believe that there are some animals that do not die. They are very simple creatures , too small to be seen without the help of a microscope. While most animals, including human beings, have billions of cells in their bodies , these little death defiers have only one. Each cell lives for a certain length of time, and then it splits to form two new animals. The adult animal turn itself into two babies .All of the new cells finally divide, but none die unless they are killed by accident or disease.

There are other cells that avoid being old. Cells from old mice have been moved into young mice over and over again, each time the body they are in wears out . In their new bodies the old cells seem to begin life over again. They divide and grow just like young cells.

Is there any way to discover the secret of these cells’ youth and apply it to human being? Not yet. But scientists are still searching, and they may be closer than ever to finding an answer. Of course , some ways to increase our chance of living longer. Like good food and exercise, have been known for years. Progress against killer disease has already raised the human life to more than seventy years, compared with less than fifty years a century ago. Now scientists are studying other ways to fight against death. They will never give up their efforts until they win their final success.

 

68. What is the passage mainly about ?

A. The law governing the growth of all creatures

B. The secret of getting old

C. Ways to begin life over again

D. Certain cells that never die

69. What does the phrase“death defiers”refer to ?

A. Animals that fear nothing                   B. Cells that can’t be understood

C. Animals that don’t die                     D. Cells that finally die in a normal way

70. Scientists are interested in these one-cell animals because they want to        .

A. find out how these tiny animals fight against diseases

B. discover the relations between human bodies and these animals

C. learn how these cells can split into new cells

D. look for ways of keeping human life much longer

71. What is the writer’s attitude towards the possibility for human beings to live longer?

A. Confident                 B. Doubtful                   C. Uncertain                 D. Respectful