In the Perry-Wolff Experiments with Harlequin Chromosomes, Colcemid Was Applied

In the Perry-Wolff experiments with harlequin chromosomes, colcemid was applied to the cells following labeling with BrdU for what reason?

A) To enhance the rate of recombination between chromatids
B) To reduce the rate of recombination between chromatids
C) To separate the chromosomes
D) As a stain
E) To stop the cells from completing mitosis