Fire officers are still trying to__the cause of the fire空里写?

Fire officers are still trying to__the cause of the fire空里写? I think they are customs officers.改为否定句是什么 They are Customs officers中的Customs,为什么开头要大写? ------my fanther and my uncle are police officers划线填空 you are fire 还是 you are fired? Customs officers executive officers His parents are police officers.They work in the police ________. there are some ____ police officers A.men's B.men C.man's D.man Those tall men are (police officers).(对括号内提问）, officers are paid so poorly that few of them bother to track down the poachers. 1.they are custom officers疑问句 .are their .（格式）2.they are Russian,一般疑问句 .they.（格式） St. ST. Fire fire fire fire