From a Stationary Position,I Observe a Moving Boxcar,which Has a Mirror

Multiple Choice

From a stationary position,I observe a moving boxcar,which has a mirror along the front wall,but it is open at the back of the boxcar.I send a flash of light from my flashlight and time the flash of light as it goes to the front of the boxcar and returns to the back of the boxcar.A passenger in the boxcar also times the round trip of the flash of light.Compare the times recorded on our watches.

A) The time recorded on his watch is longer.
B) The time recorded on the two watches is the same.
C) The time recorded on his watch is shorter.
D) The answer depends on the reference system you are in.