The correct option is B): meters A and C. In fact, both A and C are ammeters. An ammeter is a device used to measure the current in a branch of a circuit. In order to work properly, an ammeter should be connected in series to a resistor, in order to have the same amount of current that passes through the resistor. In this circuit, we see that devices A and C are both connected in series to a resistor, so they are ammeters. Instead, devices B and D are connected in parallel, so they do not measure the current but the voltage (in fact, they are called voltmeter).