They saw some street cleaners cleaning the street(对划线部分提问)

问题描述:

They saw some street cleaners cleaning the street(对划线部分提问)
划线的是some street cleaners

Whom did they see cleaning the street?理由some street cleaners 一些环卫工, 指人, 如果看成未知的应该用Whom, 因为是做宾语的