The ornamental design for a hook, as shown and described.
FIG. 1 is a first perspective view of a hook embodying the design;
FIG. 2 is a second perspective view of the hook of FIG. 1;
FIG. 3 is a front elevation view of the hook of FIG. 1;
FIG. 4 is a side elevation view of the hook of FIG. 1, with the opposite side elevation view being essentially a mirror image thereof;
FIG. 5 is a rear elevation view of the hook of FIG. 1;
FIG. 6 is a top-down plan view of the hook of FIG. 1; and,
FIG. 7 is a bottom-up plan view of the hook of FIG. 1.
The broken line showing of a portion of the hook structure is included for the purpose of illustrating environment and forms no part of the claimed design.