27. The boy was busy doing his homework, only_____once in a while to look out of the window.
Getting out of the crowded bus, ______
______ better in 2010 World Expo is the duty of every citizen in Shanghai.
She felt completely ______ during the vacation but now she has to go back to work again.
Football is very important to me, but _____ is our friendship.
At proper horse races everyone has already studied the form of the horse ______.