Questions 15 to 17 are based on the following passage. At the end of the passage, you will be giv en 15 seconds to answer the questions.
Now, listen to the passage.
Why did the couple recognize Rod’s voice on the radio immediately

A．Because Rod was the most naughty student they had ever had.
B．Because Rod now is a famous politician who always makes speech on radio program.
C．Because Rod now is a famous scientist in area of AIDS.
D．Because Rod always spoke with an unusual slow voice since he was a student.