The ornamental design for a sink, as shown and described.
In a preferred embodiment, the nature of this product is as a plumbing fixture in the form of a sink which is primarily useful for washing various items and the body parts of humans.
FIG. 1 is a right, top, front perspective view of a sink embodying our new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a right side elevational view thereof, the left side elevational view thereof being a mirror image of the right side shown;
FIG. 5 is a rear elevational view thereof; and,
FIG. 6 is a bottom plan view thereof.
The broken line representations in the figures are for the purpose of illustration only, and form no part of the claimed design.