题目

We all know that the normal human daily cycle of activity is of some 7—8 hours’ sleep alternation with some 16—17 hours’ wakefulness and that, broadly speaking, the sleep normally coincides with (与一致) the hours of darkness. Our present concern is with how easily and to what extent this cycle can be modified.The question is no more an academic one. The ease, for example, with which people can change from working in the day to working at night is a question of growing importance in industry where automation calls for round-the-clock working of machines. It normally, takes fI usually have Chinese class ____the morning and eat lunch ___ 12 o’clock. ( )A. at ; at B. in ;in C. in; at