練習：

　　1. The human heart stops producing cardiac cells

　　A when a person is born.

　　B when a person becomes old.

　　C when a person gets sick.

　　D when a person dies.

　　2. The finding could prove to be helpful to

　　A the study of longstanding mysteries.

　　B the analysis of cardiac cells.

　　C the prevention of chronic diseases.

　　D the treatment of heart disease.

　　3. The people whore in their mid-70s， only 0.45 percent of cardiomyocytes

　　A are still functional

　　B are replaced each year.

　　C are lost each year.

　　D are damaged each year.

　　4. Chronic heart failure is associated with

　　A the death of heart cells.

　　B the life span of a person.

　　C the effects of pharmaceuticals.

　　D the weight of the patient.

　　5. It remains unknown whether the rate of cell turnover in diseased hearts

　　A changes over time.

　　B can be monitored.

　　C is the same as that in healthy hearts.

　　D is high enough to replace cells faster than theyre dying off.

　　答案與解析

　　1. D 短文的第一段說，科學家們發現，在人的整個生命過程中，其心臟不斷產生新的心肌細胞。言外之意，這個過程直到人死才會停止。

　　2. D 短文的第二段說，這一發現將為心臟病的治療開辟新的途徑。

　　3. B 短文的第四段說，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，該更替率不斷下降，等到75 歲時，只有0.45%。

　　4. A 短文的倒數第三段說，慢性心衰是由心肌細胞死亡導致的。

　　5. C 短文的最后一段說，心臟產生的新細胞的數量是按著健康心臟計算的，而有病心臟的細胞更替率是否與健康心臟相同還不得而知。