---Why didn’t you go to play football with us yesterday afternoon? ----I _____my mother with housework then. A. help B. was helping C. had helped D. have been helping 答案:B为了解学生的课外作业负担情况,随机调查了50名学生,得到他们在某一天各自课外作业所用时间的数据.(见统计表),根据表中数据可得这50名学生这一天平均每人的课外作业时间为________小时.时间(小时)00.511.52人数52010105