Question

Which of these components is not necessary for current to flow in a series or parallel circuit?
a. wire
b. switch
c. resistor
d. All of these are needed.

Answer 1

All the components (D) ie, wire, switch and resistor are needed for current to flow in a series or parallel circuit.  
In a simple series circuit, all the components are connected end-to-end to form a single path for the electrons or electric current to flow through the circuit. A simple parallel circuit is where all the components in the circuit are connected between the same two sets of common points, creating a more than one path for the electrons or electric current to flow around the circuit. 

Answer 2

Only wire is necessary.

A switch is only needed if you want to be able to turn the current on and off easily.

A resistor is only needed if you want to generate some heat or limit the current.