Last month, when I walked past a fashion shop, a dress attracted my attention, so I asked my mother to buy it for me.

Last month, when I walked past a fashion shop, a dress attracted my attention, so I asked my mother to buy it for me. But my mother made a bargain with me. If I do well in the exam, she will buy it for me. So I study very hard and get the third place in my class. I get my dress and I am very happy. 
上个月，当我经过一家时装店时，一件裙子吸引了我的注意力，所以我叫妈妈给我买。但是，我妈妈和我做了一个交易。如果我在考试中取得好成绩，她才会买给我。所以我非常努力学习，最后获得了班上第三名。我得到了我的衣服，我真是太开心了。