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
Only after ___ your homework _________ watch TV.
A.have you finished; you can
B.you have finished; can you
C.have you finished; can you
D.you have finished; you can
传染源向其周围传播病原体所能涉及范围称:()。
A、疫区
B、疫点
C、传染地
D、疫源地
E.污染区