-- _____is that used for?---_____ the floor.
It’s the first time ______ he has helped us.
Here are two pairs of shoes, ______ you may choose.
He plays well or badly according to his mood (心情), so he’s a very _________ player.
No one knows exactly ______ this important discovery was made.
The weather turned out to be very good, _______ was more than we could expect.