单项选择题The Case of the Missing Trade refers to ( ) A、the 9th volume of the Hardy Boys Mystery series. B、the fact that world exports does not equal world imports. C、the fact that factor trade is less than predicted by the Heckscher-Ohlin theory D、None of the above.
多项选择题以下对于人工作业、机械化作业、综合化机械作业这三种装卸搬运方式的描述错误的有