5. A woman riding a ski lift with a constant velocity of 2.1 m/s up to the top of the hill suddenly hears a loud noise. As she turns to see a fighter jet doing acrobatics involving
sharp turns, she accidentally knocks her skis off the lift. In the moment afterwards, which two objects have the same inertial frame of reference?
"O
the skier and her skis
the pilot and the jet
the skier and the lift
the skis and the ground

Independent variable is something that is changed in a experiment. 

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

It really doesn't matter for any of the questions that you've listed.