If we do not deal with ________ problem caused by air pollution, our planet may no longer be ________ healthy place for us.

A．a; the

B．a; a

C．the; a

D．the; the

为使Word文档能在其他应用程序中调用，最好的办法是在存盘时将其存为（）格式。

A.TXT

B.DOC

C.WPS

D.DOT