Three subunits of a protein complex have been resolved in a two-dimensional polyacrylamide gel, as shown in the schematic drawing below. Indicate whether each of the following better describes the a, b, or c subunit. Your answer would be a three-letter string composed of letters a, b, and c only, e.g. cca.

( ) It has the smallest apparent molecular weight.
( ) It has the highest negative charge.
( ) It has the lowest isoelectric point.