A、It has decreased. B、It has been exaggerated. C、It has become better understood. D、It has remained basically the same. A短文开头提到，

(13)In recent years, the death rate among American centenarians—people who have lived to age 100 or older—has decreased, dropping 14 percent for women and 20 percent for men from 2008 to 2014. The leading causes of death in this age group are also changing. In 2000, the top five causes of death for centenarians were heart disease, stroke, flu, cancer and Alzheimer’s disease.(14)But by 2014, the death rate from Alzheimer’s disease for this age group had more than doubled—increasing from 3. 8 percent to 8. 5 percent—making the progressive brain disease the second leading cause of death for centenarians. One reason for the rise in deaths from Alzheimer’s disease in this group may be that developing this condition remains possible even after people beat the odds of dying from other diseases such as cancer.
     (15)People physically fit enough to survive over 100 years ultimately give in to diseases such as Alzheimer’s which affects the mind and cognitive function. In other words, it appears that their minds give out before their bodies do. On the other hand, the death rate from flu dropped from 7. 4 percent in 2000 to 4.1 percent in 2014. That pushed flu from the third leading cause of death to the fifth.
    Overall, the total number of centenarians is going up. In 2014, there were 72,197 centenarians, compared to 50,281 in 2000. But because this population is getting larger, the number of deaths in this group is also increasing—18,434 centenarians died in 2000, whereas 25,914 died in 2014.
Questions 13 to 15 are based on the passage you have just heard.
13. What does the speaker say about the risk of dying for American centenarians in recent years?
14. What does the speaker say about Alzheimer’s disease?
15. What is characteristic of people who live up to 100 years and beyond?