答案：D

考查特殊句型。祈使句+连词+陈述句=If条件句，主句。句意：在那么城市的消防部门的网站上搜索，你就会了解很多关于防火的知识。本题=" If" you search the website of the Fire Department in your city, you will learn a lot about firefighting.故D正确。