Two Blocks, a and B, Are Being Pulled to the Right

Multiple Choice

Two blocks, A and B, are being pulled to the right along a horizontal surface by a horizontal 100-N pull, as shown in the figure. Both of them are moving together at a constant velocity of 2.0 m/s to
The right, and both weigh the same. Which of the figures below shows a correct free-body diagram of the horizontal forces acting on
The upper block, A?

A)
B)
(No horizontal forces act on $A$ .)
C) $A \longrightarrow 50 \mathrm {~N}$
D) $\mathrm{A} \longrightarrow 100 \mathrm{~N}$
E)