练习：
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.
答案与解析
1. D 短文的第一段说，科学家们发现，在人的整个生命过程中，其心脏不断产生新的心肌细胞。言外之意，这个过程直到人死才会停止。
2. D 短文的第二段说，这一发现将为心脏病的治疗开辟新的途径。
3. B 短文的第四段说，一个人20 岁时，其每年被更替的心肌细胞为1%，随着年龄的增长，该更替率不断下降，等到75 岁时，只有0.45%。
4. A 短文的倒数第三段说，慢性心衰是由心肌细胞死亡导致的。
5. C 短文的最后一段说，心脏产生的新细胞的数量是按着健康心脏计算的，而有病心脏的细胞更替率是否与健康心脏相同还不得而知。