oscilloscope is the more suitable test instrument.
a. The DC voltage of a +12 V dc supply rail in a printed circuit board (PCB).
b. The RMS voltage across a resistive heater driven by a 48 V ac 60 Hz square wave.
c. The RMS current flowing in a resistor connected across the output of a function
generator (5 V pp, 800 kHz).
d. The RMS voltage across a loudspeaker with a 12 kHz sinusoidal input.