is known to us all is that the old worker, 　　　life was hard in the past, still works hard in his seventies.

A．As; whom

B．What; whom

C．It; whose

D．What; whose

下列关于乙酸的叙述错误的是（　　）

A．乙酸可使紫色石蕊试液变红

B．用乙酸除热水瓶中的水垢

C．乙酸分子中含有三个氧原子

D．食醋中的有效成分是乙酸