One way for students to prevent H7N9 flu virus is to open the windows of the classroom to allow the air to ________.
My mother is always warning me when I go out, “Don’t get off the bus ____ it is stopping.”
—Are you through with your homework? —Well, ____.
She was such a proud person that she would die ____ she would admit she was wrong.
Working in the kitchen for years made Tom ____ a good cook.
—You know Mr. Green has been ill for days? —Yes, I wonder if he is ____ better now.