The ability to regulate the amount of charge flowing in a circuit is

A. resistance.

B. direct current.

C. voltage.

D. alternating current.

So we want to know what has the ability to regulate the amount of charge that flows trough a circuit. So lets take a look at Ohms law: I=U/R. So the current, or charge per unit time, if the voltage U is constant is regulated by the resistance R. So the answer is A. resistance