The ornamental design for a refrigerator, as shown and described.
FIG. 1 is a perspective view of a refrigerator showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is right side view thereof;
FIG. 6 is a top plane view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is a reference view similar to FIG. 1, showing a state in which a right-top door of the refrigerator is completely opened.
The broken lines shown in the drawings illustrate portions of the refrigerator that form no part of the claimed design. The subject design is a partial design and the solid line shows a boundary of the portion to be claimed. The main point of the subject design is the combination of the figure and the shape of “refrigerator”.