When division of the zygote reaches the eight-cell stage and the planes of cleavage of the upper four cells line up with those of the bottom four cells so that two tiers of cells result, one directly above the other, the type of cleavage is called

A. direct cleavage.
B. spiral cleavage.
C. indirect cleavage.
D. protostome cleavage.
E. radial cleavage.