Why Is Hydrodynamic Focusing Used in Automated Cell-Counting Instruments

Why is hydrodynamic focusing used in automated cell-counting instruments?

A) To prevent coincidence passage through the detection aperture
B) To increase the visibility of the cells passing through the aperture
C) To allow for maximal light absorbance through the cells passing through the aperture
D) To ensure adequate uptake of fluorescent staining by the cells