有关于高中省略主语和谓语的问题

1.When arriving classroom,he started to do homework at once.
2.Faced with this situation,we should take measures to solve it.(为什么是Faced with,不是说主语一样可以省略主谓吗?face与we不是主动吗,为什么不用facing?）
3.Located in Handzhou,the factory is the second biggest factory in China.(为什么不用 locating?）
请问这三句话有什么区别?
三个例子都是分词短语充当状语,位于句子前部.一般是充当时间、原因、条件状语,这样的分词短语一般可以变成状语从句的.（但不总是这样的）
1.=When he arrived (his) classroom,
2.=When we were/are faced with this situation(过去现在时态均可）
3.The factory is located in Hangzhou and it is the second beginnest factory in China.(这个句子似乎不能把located称为状语,个人认为这是个地点状语.因为这确实是介绍地点的,但又不好变成状语从句）
区别：
1.主动的,保留了when
2.faced with属于固定用法,一般是be faced with面对,面临
3.这个located in一般是表示状态,相当于lie in