The best way to explore _______ countryside is on _______foot.
When _______a hand, one should say “Thank you” or “It’s very kind of you.”
Some students think it is ___ to spend some time surfing the Internet, but we shouldn’t be too dependent on it.
Not until his mother came back_______.
—What made Tom so sad? —_______.
----Are you happy that your old friend visited you yesterday? ----I would rather he_______. I was so busy then.