The parabolas y2=4x and x2=4y divide the square region bounded by the lines x=4, y=4 and the coordinate axes. If S1, S2, S3 are respectively the areas of these parts numbered from top to bottom, then S1:S2:S3 is
(A) 1 : 2 : 1
(B) 1 : 2 : 3
(C) 2 : 1 : 2
(D) 1 : 1 : 1