单项选择题我国导游服务经历的三个时期分别是( )。 A.民国以前 B.新中国成立到改革开放前 C.新中国成立以前 D.改革开放以后
单项选择题As the basic subject of international environmental law, states are divided by international, legal and institutional arrangements into developed countries and developing countries. A、正确 B、错误