Some steps in mitosis are shown below. they are not in order.

step a: spindle fibers arrange the chromosomes along the middle of the cell nucleus

step b: the cell membrane begins to close in, starting to split the cell into two

step c: chromosomes condense and begin to resemble the alphabet letter x

step d: the centromere of each chromosome splits, and chromatids move towards the opposite poles of the cell

which step represents anaphase?