The ornamental design for a refrigerator, as shown and described.
FIG. 1 is a front perspective view of the refrigerator showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a back 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 partial enlarged view of region 8, taken from FIG. 1;
FIG. 9 is a partial enlarged view of region 9, taken from FIG. 1;
FIG. 10 is a perspective view showing the state of use that the handle has been attached at the right side of the front panel, and the opening direction of the front door has been changed; and,
FIG. 11 is a perspective view showing the state of use that the front panel has been separated from the door body for clarity.
The broken lines depict portions of the refrigerator that form no part of the claimed design. The long dash-short dash-long dash broken lines on FIGS. 1, 8 and 9 depict the boundary of the enlarged view on FIGS. 8 and 9, taken from FIG. 1, and form no part of the claimed design.