You are going on a car trip with your family across the United States. To your brother's
surprise, the AM radio station that your family
is listening to is coming from a city 600 miles
away. Explain to him how this is possible. Be
sure to describe how the ionosphere affects AM
radio transmissions.​

Scientific classification

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