The correct answer is: A. Current
A parallel circuit resonance is a phenomenon that occurs when the inductive and capacitive reactances of a parallel circuit are equal in magnitude and opposite in sign. This causes the current to flow through the circuit to be amplified.
The inductive reactance of a circuit is given by the following equation:
$X_L = 2\pi f L$
where $f$ is the frequency of the current and $L$ is the inductance of the circuit.
The capacitive reactance of a circuit is given by the following equation:
$X_C = \frac{1}{2\pi f C}$
where $f$ is the frequency of the current and $C$ is the capacitance of the circuit.
When the inductive and capacitive reactances are equal in magnitude and opposite in sign, the total reactance of the circuit is zero. This means that the current flowing through the circuit is not limited by the reactance of the circuit, and the current can be amplified.
The frequency at which the inductive and capacitive reactances are equal in magnitude and opposite in sign is called the resonant frequency. The resonant frequency is given by the following equation:
$f_r = \frac{1}{2\pi\sqrt{LC}}$
where $f_r$ is the resonant frequency, $L$ is the inductance of the circuit, and $C$ is the capacitance of the circuit.
The purpose of a parallel circuit resonance is to magnify the current flowing through the circuit. This can be used in a variety of applications, such as radio receivers and amplifiers.