Solution: a, according to the geometric meaning of the inverse proportional function coefficient k, the sum of shadow areas is xy=3,

B, according to the geometric meaning of the inverse proportional function coefficient k, the sum of shadow areas is: 3,

C, according to the geometric meaning of the inverse proportional function coefficient k and the trapezoidal area method, we can get:

The shadow area is 3+1/2 (1+3) × 2-3/2-3/2 = 4.

D, according to the coordinates of points M and N and the triangle area, the area of the shadow part is: 1/2 × 1×6=3,

The maximum shadow area is 4.

So choose: C.