It is well known that the more the old people use their brains, the more mentallyactive they will be. A: 这件事传开了，老人越多用脑，智力就越灵活。 B: 大家知道了，老人更多动脑，主动性更强。 C: 众所周知，老人用脑越多，头脑就越活跃。 D: 众所周知，老人用脑越多、智力会更活跃。