The ornamental design for a rack, as shown and described.
FIG. 1 is a top, front, left perspective view of a rack showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view of the first side member thereof;
FIG. 5 is a right side view of the first side member thereof;
FIG. 6 is a right side view of a second side member thereof;
FIG. 7 is a left side view of the second side member thereof;
FIG. 8 is a top view thereof;
FIG. 9 is a bottom view thereof; and,
FIG. 10 is a top front right perspective view thereof.
The even-length broken lines depicting the remainder of the rack show features that form no part of the claimed design. The unshaded surfaces within the broken line rectangles form no part of the claimed design. The uneven-length broken lines immediately adjacent to the shaded areas in define the boundary lines of the claimed design and form no part thereof.