Question

You were late for class, but you ________ on time．

1. A.
   might be
2. B.
   should be
3. C.
   ought to have been
4. D.
   must have been

Answer 1

C
ought to have done sth．表示过去应该做而未做某事，相当于should have done sth．;must have done 表示过去肯定做过某事，故选C项。