单项选择题

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 rainfall.
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单项选择题
A．Two ways.B．Three ways.C．Four ways.D．Five ways.
A．Two ways.
B．Three ways.
C．Four ways.
D．Five ways.
单项选择题
A．Planes and motorcars have taken the place of trains.B．Oil is expensive today.C．Trains are slow.D．Railways lose money.
A．Planes and motorcars have taken the place of trains.
B．Oil is expensive today.
C．Trains are slow.
D．Railways lose money.
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