I claim the ornamental design for a sink, as shown and described.
FIG. 1 is a top perspective view of an embodiment of the claimed design;
FIG. 2 is a top plan view of the claimed design of FIG. 1;
FIG. 3 is a front elevation view of the claimed design of FIG. 1;
FIG. 4 is a right-side elevation view of the claimed design of FIG. 1;
FIG. 5 is a left-side elevation view of the claimed design of FIG. 1;
FIG. 6 is a rear elevation view of the claimed design of FIG. 1; and,
FIG. 7 is a bottom plan view of the claimed design of FIG. 1.
The ornamental design which is claimed is shown in solid lines in the drawings: The broken lines in the drawings are for illustrative purposes only and form no part of the claimed design.