In some cows the genes for brown hair (B) and for white hair (W) are CO- DOMINANT. Cows with alleles for both brown and white hair, have both
brown and white hairs (BW). Predict the PHENOTYPIC ratios of a cross
between a brown cow and a white cow.

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

The answer is periosteum