为什么“This factory produces steel.”中的steel是不可数名词?^_^

This room requires Camfrog Pro to chat.用camfrog聊天为什么显示：this room requires camfrog pro to chat how long do you stay at this factory 为什么不对? how long this factory (开办) Is this factory ______you visited last week?为什么选CIs this factory ______you visited last week?A.that B.where C.the one D.in which 1.Is this the factory----you visited last year?则用which/that 2.Is this the factory----you worked l为什么这么填呢?有什么区别? This factory is__the one___she visited yesterday.这句为什么不能用what呢?This factory is__what_____used to be owned by Mr Brown.这两句区别在什么地方呢? Is this factory (the one)I visited last week .为什么括号里不用which hat Is this factory ---you visited last Sunday?为什么填the one This is the factory ___a lot of students visited yesterday.应填哪一个词?为什么? This is the factory ___a lot of students visited.应填哪一个词?为什么? Is this the first factory the one some foreigners visited yesterday?为什么用THE ONE? 为什么“This factory produces steel.”中的steel是不可数名词?^_^ the manager and secretary are in charge of this factory 改错 还要说明为什么 Foxit Reader Pro,work like a pro!为什么要叫Foxit Reader Pro？ This is the factory where they want to visit.这个定语从句为什么用where啊?factory 不是visit的宾语吗?高手指教下. 帮忙分析下This is the factory ________ I visited yesterdayThis is the factory ________ I visited yesterday.A.that B.which C./ D.where选什么,为什么 is this factory that we visited last week,为什么在that 前加the one ,答案上说少先行词,factory不是先行词吗 This is big factory.(改为复数)