Hello你好~下面是我的回答: 1)建议把第一个句号和who was都去掉--》I once saw a cleaner cleaning on the street. 因为本身see sb doing sth就是一个常见结构,这样写就比较简洁一些 2)我觉得可以考虑把时态换成过去进行时,因为是清洁工人打扫街道的同时,那个女的在乱扔垃圾,所以可以用进行时--》But beside her, a woman was still throwing rubbish (onto the ground). 另外beside有点偏紧挨着的意思,所以也可以考虑写:But just several steps away, a woman was still throwing rubbish. 几步之外,有个女的还在扔垃圾