用a/an/the回答My mother used to be-engineer,but niw she is -bus

第一个填an,第二个填a.
决定填a或an关键取决于所修饰名词的英标,如果单词是以元音英标开头,如engineer是以元音[e]开头的,则用an.相反如果单词是以辅音开头的,如businessman以辅音[b]开头的,则用a.
而zhe和这两者的区别在于是不是特制.比如：There is a book on the desk. The book is mine. 前者不是特指,而后者却是特指前面的那一本书,所以用zhe.