Until Second World War period, some scholars only started to these economic phenomena to conduct the research, contained the underground economy research.
直到第二次世界大战期间，一些学者才开始对这些经济现象进行研究，其中也包含了对地下经济的研究。
2
It offered an useful reference for the relative project supervision in order to conduct the new "Technical Regulations of City Underground Pipeline Location" in better way.