work on ,work at.
work at , work on 表示从事于某事情，但work at为一般用语，其深度不如work on.
例如：work at math 学习数学；work on math 致力于数研究；work on some wood cuts 创作一些木刻
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为一般用语，其深度不如work on, work at a problem和work on a problem意思不大一样，前者可作学习中的“计算一道题”解，后者可引伸到生活和工作中的“研究或解决一个问题”. work out意为“计算出”.
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：选A. work out解决；work on在…上工作；work hard at + subject在…科目上努力工作.