_________ water to grow is well-known.
— Do remember to charge the mobile phone 12 hours when you first use it.— ______.
While building a tunnel through the mountains, ______.
Scientists are convinced ______ the positive effect of laughter ______ physical and mental health.
In American there are more households with pets than ______ with children.
They are said to have developed a new ______ to teaching, which is said to improve classroom teaching greatly.