I claim the ornamental design for an adjustable shelf, as shown and described.
FIG. 1 is a top perspective view of an adjustable shelf, showing my new design.
FIG. 2 is a front elevational view of the adjustable shelf.
FIG. 3 is a rear elevational view of the adjustable shelf.
FIG. 4 is a left side elevational view of the adjustable shelf.
FIG. 5 is a right side elevational view of the adjustable shelf.
FIG. 6 is a top plan view of the adjustable shelf.
FIG. 7 is a bottom plan view of the adjustable shelf; and,
FIG. 8 is a top perspective view of the adjustable shelf.
The broken lines depict portions of the article that form no part of the claimed design. The broken lines in FIG. 8 show environment of a leg structure forming no part of the claimed design. The adjustable shelf is shown with a symbolic break in its length and width. The appearance of any portion of the article between the break lines forms no part of the claimed design.