In time of serious accidents，______ we know some basic things about first aid, we can save lives.

　　A. whether          B. until　　        C. if               D. unless

In time of serious accidents，_____ we know some basic things about first aid,we can save lives.

A.whether     B.until　　 C.if       D.unless

In time of serious accidents，____we know some basic things about first aid，we can save lives.

A whether        B. until       C. if            D unless

In time of serious accidents，____we know some basic things about first aid，we can save lives.

A whether        B. until       C. if            D unless