We claim the ornamental design for a microwave oven, as shown and described.
FIG. 1 is a perspective view of a microwave oven showing our new design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a right-side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a perspective view of a microwave oven, showing a second embodiment of our new design.
The broken lines in the drawing figures are included for the purpose of illustrating environment and form no part of the claimed design. FIG. 8 is the only view showing the second embodiment. Therefore, the second embodiment includes only what is shown in FIG. 8.