The workman set fire to the factory without being noticed.
问题描述：
The workman set fire to the factory without being noticed.
变为被动语态
答
这个工人向工厂纵火,没有被人发现.The workman set fire to the factory without being noticed.变为被动语态是对工厂进行被动，还是对工人进行被动？如果是后者，原句本来就是非谓语动词的被动型态，无需变换。