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?