The author has written the passage mainly for______.
A. young children
B. experienced operators
C. common readers
D. scientists in the computer field
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Paper money printed by banks must be exchanged for metal money______demand.
A. of
B. with
C. on
D. from
Which of the following factors are very important in developing friendships?
Age and background.
B. Economic and social positions.
C. Race and looks.
D. Same interests and behavior.
A.valuableB.worthC.commonD.adequate
A. valuable
B. worth
C. common
D. adequate
______is often the case with a new idea, many preliminary activities and optimistic discussions produced no concrete proposals.
A. That
B. It
C. This
D. As