What is the composition of the Polish Air Force checkerboard?

A. Four equal squares, with the upper left and lower right being red, and the other two white
B. Four equal squares, with the upper left and lower right being blue, and the other two yellow
C. Four equal squares, with the upper left and lower right being white, and the other two red
D. Four equal squares, with the upper left and lower right being green, and the other two black
Answer: 