Tibet is facing a (an)________ task to maintain stability and all government workers must be on theirhighest guard ahead of the Tibetan New York. [ ]

Soon the hall was filled ____ people

They considered ______a computer, which was considered ______a great help in their work．

Between 1950 and 1990, the world population doubled to 5.3 . Nearly eighty of these people live in developing, poorer nations.

The old lady did not know ___________when the house caught fire.