instead of rolling down the ramp over the step, imagine the ball falls off the back of the ramp and directly to the ground. what is the amount of potential energy remaining after the ball lands on the ground

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

Attach the free body diagram and i will you answer the question.! : d

Lexy is correct because angle r is between the incident wave,  n  = 0, and a diffracted wave.