— When did you become a volunteer?

— Two years ago. I _____ this group since then. [ ]

A. joined

B. have joined

C. have been in

古希腊主张废除私有制的经济文献是( )

A．柏拉图的《法律篇》

B．柏拉图的《理想国》

C．亚里斯多德的《经济论》

D．亚里斯多德的《政治论》