l saw them were sweeping the floor at that time找出错误并改正
问题描述：
l saw them were sweeping the floor at that time
找出错误并改正
答
l saw them sweeping the floor at that time.那时候我看见他们正在扫地。
see sb doing sth，看见某人做某事
see 后面一般不接从句
答
l saw they were sweeping the floor at that time
不能用宾格them 是省略了that 的宾语从句，要用they，在从句中做主语
答
应该是
把them改为they
做从句的主语,不能用宾格,要用主格
在那时我看到他们正在扫地