The ornamental design for a brush, as shown, and described.
FIG. 1 is a front view of the brush;
FIG. 2 is a rear view of the brush;
FIG. 3 is a side view of the brush;
FIG. 4 is a top view of the brush;
FIG. 5 is a bottom view of the brush;
FIG. 6 is a perspective view of the brush; and,
FIG. 7 is a perspective view of the brush with its handle in a pivoted position.
In the Figures, the brush is shown with a symbolic break in its width and length. The appearance of any portion of the brush beyond the break line forms no part of the claimed design.