How could you increase the potential energy of the apple?

By putting an apple up on high ground. (That is 1 example)
This creates a higher gravitational force, and when it falls down it would have a lot of kinetic energy. But, if put on low ground, it wouldn't have enough potential energy to increase the kinetic energy.

You can increase the gravitational potential energy of an apple
by gluing it back onto the tree-branch that it fell from.

Actually, by just lifting it to any place higher than where you find it.

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