A plane monochromatic electromagnetic wave with wavelength λ=2.0cm, propagates through a vacuum. Its magnetic field is described by >B⃗ =(Bxi^+Byj^)cos(kz+ωt), where Bx=1.9×10−6T, By=4.7×10−6T, and i^ and j^ are the unit vectors in the +x and +y directions, respectively. What is Sz, the z-component of the Poynting vector at (x=0,y=0,z=0) at t=0?

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

No. rocks can follow various pathways.

Can you give more detail