We claim the ornamental design for a sink, as shown and described.
FIG. 1 is a perspective view of an embodiment of the claimed design;
FIG. 2 is a top view thereof;
FIG. 3 is a bottom view thereof;
FIG. 4 is a front view thereof; and,
FIG. 5 is a side view thereof.
The ornamental design which is claimed is shown in solid lines in the drawings. The broken lines in the drawings form no part of the claimed design. Broken lines formed by equal length dashes show unclaimed subject matter. Broken lines formed of unequal length dashes (i.e., dash-dot) define bounds of the claimed design. Broken away symbols having a jagged element show that no particular length of the portion is claimed.