The ornamental design for a sock, as shown and described.
FIG. 1 is a perspective view of a first embodiment of the sock.
FIG. 2 is a front view of the first embodiment of the sock.
FIG. 3 is left side view of the first embodiment of the sock.
FIG. 4 is s back view of the first embodiment of the sock.
FIG. 5 is a right side view of the first embodiment of the sock.
FIG. 6 is top view of the first embodiment of the sock.
FIG. 7 is bottom view of the first embodiment of the sock.
FIG. 8 is a perspective view of a second embodiment of the sock.
FIG. 9 is a left side view of the second embodiment of the sock; and,
FIG. 10 is a back view of the second embodiment of the sock.
The broken lines in the figures showing a user's foot and ankle are for the purposes of illustrating environmental structure and form no part of the claimed design.