Could you please open the door for me —Sorry, I ________, I have no key to the door.

I don’t become a serious climber until the fifth grade, ______ I went up to rescue a kite that was stuck in the branches of a tree.

I always look out when crossing the street.— You’re right. You cannot be too __________ .

Are Mr. and Mrs. Wang living alone in the house–Yes, although they have three sons, ________of them live with their parents.

A team of Americanscientists has found a treatment to protect humans from the deadly H5N1 fluvirus, ________ brings great ________ to the world.