单项选择题

It is well-knOWD that the more the old people use their brains the more mentally active 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,老人更多用脑,主动性更强。
C. 众所周知,老人用脑越多,智力就越活跃。
D. 众所周知,老人用脑越多,智力会更活跃。