焦油加工的主要任务是获得酚、萘、蒽等纯产品和()等粗产品。
参考答案:洗油沥青
Questions 1-4
When was the Endangered Species Act passed?()
A.In the f9th century.
B.In 1973.
C.In 1998.
D.In the 21st century.
常用磨料有哪三类?分别用于什么情况?