Why have the buildings of Siena been preserved and not modernized?

Choose the best paraphrase of bashes haiku an old silent pond a frog jumps into the pond splash silence again a.the pond was silent until the frog jumped in splashing now alternates with quiet b.a pond will never be silent after one frog jumps into it and starts splashing around c. a frog jumps into a quiet pond there is a splash then all is quiet once more d. there was once an accident body of water that a frog splashed into and died