问题
选择题
--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
答案
答案：D
由“since then”可知，此句时态为现在完成时，故排除AB，又因为join为非延续性动词不可与现在完成时连用，排除C，故选D