Suppose I Push a Block Along a Tabletop at a Constant

Multiple Choice

Suppose I push a block along a tabletop at a constant velocity. If I exert a constant forward force of $\vec{F}$ on the block and push it through a distance $D$ , I do work on the block equal to $|F| D$ . Since the block's kinetic energy does not change, friction must be exerting a backward force on the block of the same magnitude as $\vec{F}$ (so that the net force on the block is zero, as required to maintain the block's constant velocity) . What work does the friction force do on the block?

A) No work
B) $-|\vec{F}| D$
C) $+|\vec{F}| D$
D) Some negative work, but we need more information to determine exactly how much.
E) Some positive work, but we need more information to determine exactly how much.