You have several electrical units listed there:
a). C often used to represent a Capacitance.
b). 'A' often represents 'Ampere', the unit of Current.
c). 'R' often used to represent a Resistance.
d). 'E' often used to represent a Voltage (Electromotive Force).
Not to mention ' A. C ', a whimsical offering,
reminiscent of 'Alternating Current'.