work on ,work at.
work at , work on 表示從事于某事情，但work at為一般用語，其深度不如work on.
例如：work at math 學習數學；work on math 致力于數研究；work on some wood cuts 創作一些木刻
1. Mr Zhao, an English teacher, sat up far into the night,          a paper on how to teach beginners of English.
A. and worked at         B. and worked on     C. working at        D. working on
解：答案：D. work at為一般用語，其深度不如work on, work at a problem和work on a problem意思不大一樣，前者可作學習中的“計算一道題”解，后者可引伸到生活和工作中的“研究或解決一個問題”. work out意為“計算出”.
2. You will have to work         the weak points in your English if you want to pass the examination.
A. out          B. at         C. for        D. on
解：選A. work out解決；work on在…上工作；work hard at + subject在…科目上努力工作.