The ornamental design for a bag, as shown and described.
FIG. 1 is a top, front, right side perspective view of a bag showing our new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a rear elevation view thereof; and,
FIG. 6 is a left side elevation view, the right side elevation view being a mirror image of FIG. 6.
The broken lines that are contained within or border a stippled area illustrate stitching that forms no part of the claimed design. The broken lines in FIGS. 1-7 that are not contained within or do not border a stippled area illustrate portions of the bag that form no part of the claimed design.
The stippled areas have differing stipple densities to illustrate contrasts in surface texture between the areas with differing stipple densities.