This may seem like 'trick' question but, hopefully a deeper understanding reveals that it is not 'a trick':
Less obviously, all circuits only really require one wire if you think of them as a simple loop.
Video: Resistance & Single Wire Circuits
A single wire, a resistor, or anything that connects positive + negative terminal (including a 'short')
When current is flowing in a wire circuit, it accelerates when there is no resistance in the circuit. The unrestrained acceleration often leads to over-heating and is therefore dangerous and to be avoided.
WHY ARE TWO WIRES NEEDED?
This question can be mostly understood by considering an analgous question:
When you need to set up a pulley and belt system that rotates in a loop, are two belts needed?
The answer: Two belts are not required: There is only one belt, and the belt forms a circular loop. It looks like there are two belts, with one of them flowing leftwards and the other one flowing right. But in truth, there is just one belt, and it is rotating.
So, why are two wires needed?
The answer: There are not two wires!
Instead there is only one wire, but it is connected in a circle. All metals are full of movable electrons, so when we connect a wire in a circle, we are forming a kind of “electric drive-belt” which can move inside the wire.
But household electric outlets have three prongs!
Yes, but only two of them are used. The third one is only used for safety purposes.