The story happens _____a cold morning.
There will be a stamp show in the museum ______ we visited last week.
—As a member of bus drivers, I am proud of Wu Bin.—___________. He is a hero in my heart.
— Do you believe that paper is made _______ wood?—Yes, I do. And you can see that books are made________ paper.
— Do you know ________ this afternoon?— I'm not sure, but I'll tell you as soon as she ________.
If there is ______ pollution, the air in our city will be ________ dirtier.