Difficult Question

The pretty coed was shocked when the biology professor asked her, "What part of the human anatomy enlarges to about 10 times its normal size during periods of emotion or excitement?"

"I - I - I refuse to answer that question," the girl stammered and blushingly turned her face away.

Another student was asked the same question and answered correctly, "The pupil of the eye."

"Miss," said the professor, "your refusal to answer the question leads me to three conclusions:
1. You didn't study last night's assignment,
2. You have a dirty mind, and
3. Your marriage will be a tremendous disappointment."