There are eight tips in Dr.Roger's lecture on sleep,and one of them is:________ to bed early unless you think it is necessary.
It is said _________ was how Chinese characters developed.
The coin was almost worthless. So it was of small ________.
She had hardly got back to the kitchen ________ the doorbell rang.
They discovered the cause of the fire accidentally. They discovered it _______.
They lost their way in the mountain and _________ made matters worse was _______ it was getting dark.