(    ) 是人体中必需的一种常量元素，其中99%用来构成骨骼和牙齿。
A、钙
B、硒
C、铁
D、锌

A．Compared with Britain, Holland and France in many aspects
B．Use numbers, measurements, and dimensions to illustrate the problem
C．Serving the British colonial strategy
D．It is the representative work of political arithmetic school