Questions 18 to 20 are based on the following passage. At the end of the passage, you will be given 15 seconds to answer the questions.
Now, listen to the passage.
Dr. Jarvik’s studies showed that

A．they lost a little ability to reason over the years.
B．there is no decline in knowledge or reasoning ability.
C．their memory was not as good as it had once been.
D．their minds became a bit more active as they grew older.