Why did the author work on Christmas Eve when he first took a job in a small community hospital? 当作者在一家小型社区医院有了第一份工作时，为什么他在圣诞前夜上班?
选项：

A: He wanted to accumulate experience. 他想积累经验。
B: He had no choice on matters of shifts. 在轮班问题上他没有选择。
C: He was used to spending the night in hospital. 他习惯于在医院里过夜。
D: He had just completed his residency. 他刚刚完成了他的实习期。