The ornamental design for a monitor, as shown and described.
FIG. 1 is a perspective view of a monitor showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof;
FIG. 8 is a perspective view thereof in a condition that a mobile phone has been docked; and,
FIG. 9 is a perspective view thereof showing the state that the mobile phone docking terminal part has been closed when the subject design is not in use.
The broken lines show unclaimed subject matter only and form no part of the claimed design. The dash-dot broken lines define the bounds of the claimed design and form no part thereof.