The ornamental design for a sink, as shown and described.
FIG. 1 is an upper front perspective of a sink embodying my design;
FIG. 2 is a lower rear perspective of the sink shown in FIG. 1;
FIG. 3 is a front elevation of the sink shown in FIGS. 1 and 2;
FIG. 4 is a right side elevation of the sink shown in FIGS. 1-3, with the opposite side elevation being a mirror image thereof;
FIG. 5 is a rear elevation of the sink shown in FIGS. 1-4;
FIG. 6 is a top view of the sink shown in FIGS. 1-5; and,
FIG. 7 is a bottom view of the sink shown in FIGS. 1-6.
The broken lines showing drain openings, plumbing features, and sink surfaces are for environmental purposes only and form no part of the claimed design.