单项选择题

M:I sent a letter to make a reservation for a single room a few days ago.
W:Im sorry,but your request arrived too late.There me some conferences in town this week and were full up.
Q:Why couldnt the man book a room as he wished?()

A.Because all rooms are taken.
B.Because many spare rooms are available.
C.Because there are only double rooms.
D.Because there is just a single room.