A. Jerry stayed in a room on the third floor for an hour.
B. Jerry was absent when the discussion was being held.
C. Nobody but the woman noticed that Jerry was absent.
D. Jerry did not leave room 405 until an hour had passed.

A. Because they lack self-discipline in their studies.
B. Because they spend too much time on the Internet.
C. Because they have not exerted their utmost efforts.
D. Because they have developed poor relationships with teachers.