What is the physical meaning of the so-called "generator" of infinitesimal canonical transformation? (you may consider rotation or translation.)

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 to the question is (a)   

Well in that case, since an object moves with a constant velocity, there will be no acceleration as it is not increasing in speed.