6．On       way home, the taxi driver slowed down to make         way for an old man, who was crossing the street．

A．the; aB．the; 不填 C．不填；不填 D．the; the

7．—Have you found your book yet?

— No．I’m not sure where I         it．

A．leave              B．had left   

C．could have left  D．was to leave