I believe that it would be B (reloj) since it is talking about how there is a window, a door and then a clock in a classroom.
It is also giving you the masculine singular form indicating that it can only be reloj.
Answer:
its "Ellos se duermen en La Medianoche" yea and u got the "Ellos" and "duermen" correct just put it like "Ellos se duermen en la Medianoche"
