閱讀理解（第3l～45題，每題3分，共15分）

　　請根據(jù)短文內(nèi)容，為每題確定1個最佳選項。

Human Heart Can Make New Cells

　　Solving a longstanding mystery, scientists have found that the human heart continues to generate new cardiac cells throughout the life span, although the rate of new cell production slows with age.

　　The finding, published in the April 3 issue of Science, could open a new path for the treatment of heart diseases such as heart failure and heart attack ,experts say.

　　"We find that the beating cells in the heart, cardiomyocytes, are renewed, " said lead researcher Dr. Jonas Frisen, a professor of stem cell research at the Karolinska Institute in Stockholm, Sweden. "It has previously not been known whether we were limited to the cardiomyocytes we are bom with or if they could be renewed." he said.

　　The process of renewing these cells changes over time, Frisen added. In a 20-year-old, about 1 percent of cardiomyocytes are exchanged each year, but the turnover rate decreases with age to only 0. 45 percent by age 75.

　　"If we can understand how the generation of new cardiomyocytes is regulated , it may be potentially possible to develop pharmaceuticals that promote this process to stimulate regeneration after for example, a heart attack, " Frisen said.

　　That could lead to treatment that helps restore damaged hearts.

　　"A lot of people suffer from chronic heart failure," noted co-author Dr. Ratan Bhardwaj.

　　Ratan Bhardwaj, also from the Karolinska Institute. " Chronic heart failure arises from heart cells dying, "he said.

　　With this finding, scientists are "opening the door to potential therapies to having ourselves heal ourselves, " Bhardwaj said. " Maybe one could devise a pharmaceutical agent that would make heart cells make new and more cells to overcome the problem they are facing."

　　But barriers remain. According to Bhardwaj , scientists do not yet know how to increase heart cell production to a rate that would replace cells faster than they are dying off, especially in older patients with heart failure. In addition, the number of new cells the heart produces was estimated using healthy hearts-whether the rate of cell tumover in diseased hearts is the same remains unknown.

　　31. The human heart stops producing cardiac cells

　　A. when a person becomes old

　　B. as soon as a person gets sick

　　C. immediately after a person is born

　　D. once a person dies

　　32. The finding could prove to be useful to

　　A. the analysis of cardiac cells

　　B. the prevention of chronic diseases

　　C. the treatment of heart disease

　　D. the study of longstanding mysteries

　　33. In people in their mid-70s, only 0. 45 percent of cardiomyocytes _ .

　　A. are still functional

　　B. are reduced each year

　　C. are replaced each year

　　D. are damaged each year

　　34. Chronic heart failure is attributed to

　　A. the dying heart cells

　　B. the effect of pharmceutical

　　C. the weight of a patient

　　D. the life span of a person

　　35. It is not known yet if the rate of cell turnover in diseased hearts

　　A. is high enough to replace cells faster than they're dying off

　　B. is of any use to researchers

　　C. is the same as that in healthy hearts

　　D. changes over time

　　參考答案及解析

　　31.D [解析]根據(jù)是第一段中：…the human heart continues to generate new cardiac cells throughout the life span。在人的整個生命進程中，其心臟不時產(chǎn)生新的心肌細胞。言外之意，這個過程直到人死才會停止。

　　32.C [解析]根據(jù)是第二段中：The finding，…，could open a new path for the treatment of heart diseases 這一研究成果將為心臟病的醫(yī)治開拓新的途徑。

　　33.C[解析]第四段說，一個人20歲時，其每年被更替的心肌細胞為1%，隨著年齡的增長，該更替率( turnover rate)不斷下降，等到75歲時，只有0.45%。

　　34.A [解析]倒數(shù)第三段說：Chronic heart failure arises from heart cells dying。慢性心衰是由心肌細胞死亡導致的。

　　35.C[解析]最后一句說：心臟產(chǎn)生的新細胞的數(shù)量是按照健康心臟計算的，而有心臟病的細胞更替率是否與健康心臟相同還不得而知。

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