We must show concern ____ each other.
John, look at the time. ________ you play the piano at such a late hour?
He looked as though he _________ a ghost(鬼).
He stood for an instant with his hand still ___________.
_____ is known to all, the age _______ children can go to school is seven.
He told me that he was very familiar _______ the surroundings there and I told him that the people there were familiar _____ me.