The ornamental design for a refrigerator, as shown and described.
FIG. 1 is a perspective view of a refrigerator, showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left-side view thereof;
FIG. 5 is a right-side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a partially-exploded perspective view of FIG. 1, in which certain unclaimed elements are separated to further illustrate the claimed design; and,
FIG. 9 is a partially-exploded front view of FIG. 2, in which certain unclaimed elements are separated and not shown to further illustrate the claimed design.
The broken lines are for unclaimed environmental purposes only and form no part of the claimed design. The shade lines in the figures show contour and not surface ornamentation.