Which describes one effect of the sea-level change that occurred during the last ice age? A. flooding that swept across the land due to regression
B. buildup of salt in freshwater areas due to transgression
C. extinction of organisms in shallow waters due to regression
D. erosion of shorelines and other coastal areas due to transgression

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