In a classroom demonstration, a teacher discussing the air in the room as an ideal gas slides a solid barrier of negligible thickness into place, cutting the room into two equal-sized volumes. What is the air pressure for the portion of the room in which the teacher is standing, assuming the original pressure in the whole room was P? Treat the room as a sealed container.
(A) 41P (B) 21P (C) P (D) 2P (E) 4P