The ornamental design for a bed, as shown and described.
FIG. 1 is a perspective front view of the bed;
FIG. 2 is a perspective left side view of the bed, the right side being a mirror image thereof;
FIG. 3 is a rear view of the bed;
FIG. 4 is a perspective left side view of the bed showing a mattress support in a fully raised position, the right side being a mirror image thereof;
FIG. 5 is a perspective front view of the bed showing the mattress support in the fully raised position, the right side being a mirror image thereof;
FIG. 6 is a perspective left side view of the bed showing the mattress support in an intermediate raised position, the right side being a mirror image thereof; and,
FIG. 7 is a perspective front view of the bed showing the mattress support in the intermediate raised position, the right side being a mirror image thereof.