I heard him ____ (sing) when I passed his room填什么、、、、

问题描述:

I heard him ____ (sing) when I passed his room填什么、、、、
老师说应该填singing、、我觉得应该填was singing呢

singing :这个是对的
wassinging这个结构的话要有一个主语,him不能做主语,故不能用was singingI神马不能作主语吗》、、、我乱了、、him 是代词的宾格,自然是作宾语啊,故不能用主语原句改成:he was singing when I passed his room就对了he能作主语的