单项选择题

Questions 14 to 17 are based on the following passage. At the end of the passage, you will be given 20 seconds to answer the questions.
Now, listen to the passage.

According to the passage, the island’s deafness rate has fallen in the twentieth century because

A.the patterns of marriage have changed.
B.many deaf people have regained their hearing.
C.most of the original population has left the island.
D.the island has become famous for its research facilities.