With everyone’s face_________behind the mask, it’s hard to tell who they really are.

A．having hidden

B．being hidden

C．hidden

D．hiding

“阴胜则阳病”所体现的阴阳失调关系是（）。

A.对立制约

B.相互依存

C.相互促进

D.相互转化

E.相互为用