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.
Why was the survey based on the scores of a math exam
A．Because math was the most difficult course. B．Because it was a federal exam and is fair. C．Because math could reflect the teaching quality in a better way. D．Because all students took the math exam.