单项选择题
[听力原文]
W: I’m in trouble. I have to get these letters to the post office before it closes at 6, and it’s almost 6:00 already.
M: Take it easy. This clock is 20 minutes fast, so you still have 30 minutes
A．At 6:30 p.m.
B．At 5:50 p.m.
C．At 5:30 p.m.
D．At 6:50 p. m.