1. The resistor is located at point D.
A resistor is an element of a circuit that opposes to the flow of current through it: the value of its resistance (R) tells how much the resistor opposes to the flow of current, and the resistance is related to the voltage in the circuit (V) and the current (I) by the Ohm's law:
Resistance is measured in Ohm (), and a resistor is usually represented with a zig-zag line as the one at point D.
2. The switch is located at point B.
A switch is an element of the circuit that can be switched on and off, opening and closing the circuit, therefore allowing or not the flow of current through it. When the switch is open, no current flows; when it is closed, the current can flow through the circuit.
The symbol of a switch is represented at point B.