Given below is a circuit showing current flowing in it. Identify each component $A, B, C, D$ of this circuit.

(N/A) Based on standard circuit symbols:
$A$ represents an electric bulb,which is a load in the circuit.
$B$ represents a rheostat (variable resistor),used to control the current in the circuit.
$C$ represents an electric cell,which acts as the source of potential difference.
$D$ represents an ammeter,which is used to measure the electric current flowing through the circuit.