The ornamental design for a clock, as shown and described.
FIG. 1 is a top, front, right perspective view of a clock showing our new design;
FIG. 2 is a top, rear, right perspective view thereof;
FIG. 3 is a top, front perspective view thereof;
FIG. 4 is a front elevation view thereof;
FIG. 5 is a right side elevation view thereof, a left side elevation view being a mirror image of the right side elevation view; and,
FIG. 6 is a top plan view thereof.
The broken lines shown in the drawings illustrate portions of the clock and form no part of the claimed design.
The phantom lines shown in FIG. 2 illustrate portions of the clock that are seen through a transparent, window portion of the clock housing and form no part of the claimed design.