The ornamental design for a fork, as shown and described.
FIG. 1 is a perspective view of a fork according to a first embodiment;
FIG. 2 is a front-side elevation view thereof;
FIG. 3 is a rear-side elevation view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines shown on the drawings depict portions of the fork that form no part of the claimed design. The dash-dot-dash lines define the bounds of the claimed design and form no part thereof.