By looking at a problem in as many ways as possible，creative thinkers can find solutions that would

_________remain invisible.[ ]

A．otherwise  

B．yet  

C．already  

D．forever

在导游语言中，有声而无固定语义的语言称为是（）。

A.口头语言

B.副语言

C.书面语言

D.态势语言