单项选择题
M: Look, the lights in the lab are still on. It must be Professor Zhang who is still in it.
W: How could it be I saw her go home just a moment ago.
A. Professor Zhang couldn’t be in the lab.
B. Professor Zhang forgot to turn off the lights in the lab.
C. Professor Zhang went home a long time ago.
D. Professor Zhang was the last one to leave the lab.