— Where do these books ______?

— Put them back ______ they were.

A．go; where

B．lay; where

C．lie; to where

D．place; to which

下列含有非极性键的共价化合物是(    )

A．HCl

B．Na₂O₂

C．C₂H₂(两个碳原子间成叁键)

D．CH₄