What is the grand drape in a proscenium theatre?

a
The area between the stage and the first row of the audience seating.
b
The extended portion of the stage that projects towards the audience.
c
The large arch or rectangular opening between the stage and the audience seating area.
d
The large curtain located just behind the proscenium arch, raised or lowered to reveal or conceal the stage before and after performances or during scene changes.

d

The large curtain located just behind the proscenium arch, raised or lowered to reveal or conceal the stage before and after performances or during scene changes.