单项选择题

B
根据下面短文回答下列问题。
There were three professors at the railway station. They were deep in conversation. The train had just arrived, but they didn’t see it. Then the guard (列车员) shouted (喊道), "Take your seats, please!"
The professors heard the shouts and rushed for the train. Two of them got on the train before it moved. The third one was left behind. He looked sad. One of his students was at the station. He told the professor, "It wasn’t too bad, sir. Two out of three got on the train."
But the professor said, "It was my train. My two friends only came to say goodbye.\
The student thought it was not too bad because ______.