《1990年通则》将所解释的贸易术语分成（）。
A.二组
B.三组
C.四组
D.六组
参考答案：C
The billionaire ______ all his possessions to his son when he died.
A．write down
B．get down
C．handed down
D．turn down
简述洛氏硬度测量法的优缺点
