Question

He was heard_______just now. What happend?

Answer 1

有be heard doing 的用法。请看例句：
1. I often hear him sing in the morning. (改为被动语态）(我经常听到他早晨唱歌，hear sb. do sth. ）
He is ofen heard to sing in the morning.
2. I heard him singing just now. (改为被动语态）("刚才我听到他正在唱歌”hear sb. doing sth.）
He was heard singing just now.
我是复制别人的。

Answer 2

被动式，把句子反过来，就是hear he（him）____。句式是hear somebody doing。