Due to Chloride Active Transport in the Gills of Freshwater

Due to chloride active transport in the gills of freshwater fish, the epithelial cells of the gills

A) become increasingly negative because chloride ions are negative.
B) become increasingly positive because chloride ions are positive.
C) are neutral because each chloride ion is exchanged with a sodium ion.
D) are neutral because each chloride ion is exchanged with a bicarbonate ion.