单项选择题

M: Mary, How long does it take you to drive home when there is not much traffic
W: Only twenty minutes. But if I can’t leave my office before 11:00 a. m. , it sometimes takes me forty minutes.

How long does it take Mary to drive home when it isn’t rush hour()

A. 20 minutes.
B. 30 minutes.
C. 40 minutes.
D. One hour.