You are magically able to map where the sand grains go for over a few years on an east coast beach. most of the motion is:
a. toward the shore in the summer, and away from the shore in the winter.
b. toward the shore in the winter, and away from the shore in the summer. into deep water.
c. along the shore, in the longshore drift.
d. toward and away from the shore with individual waves.

D) Toward and away from the shore with individual waves.

Explanation:

D) Toward and away from the shore with individual waves.

Reason: A beach sand grain spends most of its time coming in, going out, coming in, going out, and not getting anywhere. A tiny bias exists, such that the in and out will move slightly along the coast, and will cause seasonal changes, and will move some sand to deep water.

a and b because with the other three, they simplify to something else.