A．To check the accuracy of scales.
B．To calculate the density of other metals.
C．To observe changes in the atmosphere.
D．To measure amounts of rain fall.
A．Someone spilled water on it.
B．Someone broke it
C．It was imprecise.
D．The standard for measuring was changed.
A．It is a small amount to pay for so much precious metal.
B．It is difficult to judge the value of such a weight.
C．It is reasonable.
D．It is, too high for such a light weight.