--When did you become a volunteer for the elderly?

-- Two years ago. I        this group since then.

A．joined

B．took part in

C．have joined

D．have been in

关于生长发育的阶段性和程序性，下列说法不正确的是

A．生长发育是一个连续的过程

B．生长发育是质变的过程

C．生长发育中有不同的发育阶段

D．生长发育的各阶段顺序衔接，不能跳跃

E．生长发育的任何阶段受到阻碍都会对后一阶段产生不良影响