te 2.1 Forces of 10N horzontally lly to the left and 13N in the opposite direction 1N and 5N both vertically upwards. draw using a Cartesian plane

The independent variable would be the fertilizer as it is what the dependent variable (the growth of grass) depends on.

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.