Many clothing manufacturers now substitute artificial silk _____ natural silk to cut down costs of production.
_______ different life today is ________ what it was 30 years ago.
A man may usually be known by the books he reads _____ by the friends he keeps.
Although he is often tired _____ his work, he is never tired _____ his job. In fact, he enjoys it.
Is it true _____ the rain stops, it will be as hot as in the summer here?
— Is your mother still a teacher? — ______.