1 . The abacus was invented in China thousands of years ago. It is usually made of wood and has many beads. By _____________the beads up or down, one can finish lots of math problems. It is a joy to watch an old man use an abacus. Fingers move, beads knock, and the _____________comes out a few seconds later. However, it requires lots of _____________to use the abacus well. In the past, the use of the abacus was taught in all schools. It usually takes the students several years to master this skill completely.

Today, abacuses have become a _____________although they are no longer widely used. Abacuses used to be a must-have for businessmen, _____________some people believe that abacuses are helpful for gathering wealth.