The ornamental design for a refrigerator, as shown and described.
1. Refrigerator
1.1 : Perspective
1.2 : Front
1.3 : Back
1.4 : Left
1.5 : Right
1.6 : Top
1.7 : Bottom
1.8 : Perspective view with the outer door open
1.9 : Perspective view with the outer and inner doors open
The broken lines depict portions of the refrigerator that form no part of the claimed design; reproduction 1.1 is a front perspective view of the refrigerator; reproduction 1.2 is a front view thereof; reproduction 1.3 is a back view thereof; reproduction 1.4 is a left view thereof; reproduction 1.5 is a right view thereof; reproduction 1.6 is a top view thereof; reproduction 1.7 is a bottom view thereof; reproduction 1.8 is a perspective view thereof in a condition that the outer door of the double door is opened; reproduction 1.9 is a perspective view thereof in a condition that the both inner and outer doors of the double door are opened; this is a design for a refrigerator made of glass, synthetic resin and metal; the claimed design has a double door (door-in-door) as shown in reproductions 1.8 and 1.9.