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.
A．How to care for precious metals. B．A standard unit for measuring weight. C．The value of precious metals. D．Using the metric system.
A．He drives too fast. B．He plays his guitar too loudly. C．His radio wakes her children up. D．His friends are too noisy.