The ornamental design for a hook, as shown and described.
FIG. 1 is a perspective view of a hook according to the invention showing the top, back and side.
FIG. 2 is a top view of the hook.
FIG. 3 is a bottom view of the hook.
FIG. 4 is a right side view of the hook.
FIG. 5 is a left side view of the hook.
FIG. 6 is a front view of the hook; and,
FIG. 7 is a back view of the hook.
The dot dash dot lines immediately adjacent to the shaded areas represent bounds of the claimed design. The broken lines in the drawings illustrate portions of a hook which form no part of the claimed design.