16.A. dates B. make sure C. necessary D. use E. make of |
Even before humans could read or write, they needed to count. First they used their fingers, but when they had to deal with figures over ten, a counting device became (1)
.
The earliest known calculating device is probably the abacus. It (2)
back at least 3,000 years ago and the abacus has been used for centuries by merchants, clerks, students and accountants. It is still in (3)
today, particularly in Asia. In fact, the abacus has been around so long that even the smartest historians can't (4)
who invented it. What we do know is that it was used by Egyptians, Persians, Chinese, Greeks, Romans and more.