One possible version:：

Last week , our class was  on duty in the cafeteria for student self-management. On the first day ,I  was shocked to see so much leftover food thrown away by students, what a waste! Being concerned about it , my classmates and I had a beated discussion on how to solve the problem. Lots of good ideas came up, such as holding class meetings, putting up wall newspapers and changing a fine for wasting food . finally , we all agreed that wall newspaper would be the best choice.

The next day , we put our idea into reality. Towards lunch time, we put up a wall newspaper outside the school cafeteria, calling on students not to waste food . many students gathered around to read and  expressed their support. To my great delight, there were changes soon, in the cafeteria, I found the trays returned after lunch all empty without any leftover, food was saved and the dining hall was cleaner. seeing this ,I felt relieved and proud of what we had done.

试题解析：从文章体裁分析，本文是一篇记叙文的写作，写的是在学校食堂值班时看到一些学生浪费食物的现象，根据图画内容叙述帮助减少这种现象，减少食物浪费。

【亮点说明】

文章使用了非常好的短语和句子给文章增色，如be shocked  to see so much leftover food thrown away(be shocked to do sth 因为。。。而感到震惊，see + 宾语 +  done 表被动) ，what a  waste ! 感叹句calling on students not to waste food（call on sb to do sth 呼吁某人做某事）！To my great delight使我非常高兴的是（to one’s + 名词，使某人。。。的是 ），seeing this ,I felt relieved and proud of what we had done.（ doing 做状语，feel + done 感到。。。be proud of 以。。。为自豪 what引导的名词性从句）等。