A good teacher must be able to help his students learn the subject with great interest ______ he reaches the last minute of the class.

What is the instrument used for— It’s used for ____________ steel.

When we saw her in the street, westopped ______ to her.

Some people like wearing fashionable clothes;______, some birds like bright feathers.

What do you think of the bridge—I have never seen _________ before.