题目

Bob和弟弟度过了一个愉快的周末。他们都做了些什么呢？参考表格所给短 语，与一篇50词左右的短文。Saturday morning Saturday afternoon Sunday morning Sunday afternoon washed their schoolbags went to a park did homework played football read books watched TV went fishing saw a film 答案：Bob and his brother had a nice weekend. On Saturday morning they washed their schoolbags. Then they went to a park. On Saturday afternoon, they did homework. Then they played football. On Sunday morning, they read books. Then they watched TV. On Sunday afternoon, they went fishing. Then they saw a film.用已知浓度的高锰酸钾溶液滴定未知浓度的硫酸亚铁酸性溶液时应            指示剂，原因是                                                                                                       .