---what time do you usually go to bed?

问题描述:

---what time do you usually go to bed?
--- It ___,but on weekends i always go to bed late and sleep late.
A.differs B varies C.changes
为什么c不能选呢.谁能解释下.

时间是不确定,而不是时间在变,这样理解吗?这里的it是指时间,而不是作息.