The origins of human speech remain a mystery,__________ we have a fairly accurate idea of when writing began.
What can we infer from the last paragraph?
原始社会以群居为主,有了猎物一起分,体现了原始社会教育的()
最近发展区理论的提出者是()
在学生咨询中,( )是着重训练行为的方法。