Why is a car rounding a curve accelerating, even if it is moving at a constant speed?

Automobile speedometers give an instantaneous velocity. It is important to remember that because the velocity has a direction, a change in either the speed or the direction results in a change in velocity. This leads to an interesting fact, a car going around a curve can have a constant speed and yet still have a changing velocity. The car in the following diagram is traveling around a curve. Suppose the driver looks at his speedometer when the car is at points "A", "B", and "C". At each of these points he notices that the speedometer reads 30km/h. His speed is a constant 30km/h as he rounds the curve. Now look at what is happening to his direction of motion. As he goes around the curve, his direction changes from East to South. Because of this change in direction, we have to conclude that his velocity is changing even though his speed is constant.

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current