He used not to work hard．When the teacher had class，he pretended to listen to the teacher carefully．
表示过去习惯于做某事可用used to+动词原形，否定形式可以写成used not to do，所以本题的第一句可翻译成He used not to work hard。本题的第二句含有时间状语从句，可以用when来引导，本题描述的是过去，要用过去时，故老师上课可以翻译成the teacher had class，假装做某事可翻译pretend to do，听课可以翻译成listen to the teacher，修饰动词听应该用副词carefully，故本题的第二句可翻译成When the teacher had class，he pretended to listen to the teacher carefully。