Air, or _______ is called the atmosphere, surrounds the whole world.
_______ is our belief that improvements in health care will lead to a stronger, more prosperous economy.
He is only thirty, but has got _____.
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_______.