A Block of Mass M Slides Down a Frictionless Plane

Multiple Choice

A block of mass M slides down a frictionless plane inclined at an angle θ with the horizontal. The normal reaction force exerted by the plane on the block is

A) Mg.
B) Mg sin θ.
C) Mg cos θ.
D) Mg tan θ.
E) zero, since the plane is frictionless.