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 showing the use state in which the window on the outer door has been transparent
1.9 : Perspective view 2
1.10 : Front view 2
1.11 : Back view 2
1.12 : Left view 2
1.13 : Right view 2
1.14 : Top view 2
1.15 : Bottom view 2
1.16 : Perspective view showing the use state in which the mini-table has been unfolded
1.17 : Perspective view 3
1.18 : Front view 3
1.19 : Back view 3
1.20 : Left view 3
1.21 : Right view 3
1.22 : Top view 3
1.23 : Bottom view 3
The broken lines depict portions of the refrigerator that form no part of the claimed design; reproductions 1.1 to 1.7 are the front perspective, front, back, left, right, top and bottom views of the refrigerator in a condition that the doors are closed; reproduction 1.8 is a perspective view showing the use state in which the window on the outer door has been transparent; reproductions 1.9 to 1.15 are the front perspective, front, back, left, right, top and bottom views in a condition that the window of the outer door is opened; reproduction 1.16 is a perspective view of reproduction 1.9 showing the use state in which the mini-table has been unfolded; reproductions 1.17 to 1.23 are the front perspective, front, back, left, right, top and bottom views in a condition that the double door is opened; this design is for a refrigerator with a double door (door-in-door), and the outer door is a see-through type window; the see-through window is normally opaque but it turns to be transparent by the user's touch or the operation of the access sensor as shown in reproduction 1.8; at the opposite lower part of the window, there is a mini-table which can be unfolded as shown in reproduction 1.16.