Gunpowder is generally believed in ancient China.
A. to have invented
B. being invented
C. to have been invented
D. having invented
网友回答
A. to have invented
B. being invented
(答案→)C. to have been invented
D. having invented
解析： 考查固定搭配。Be believed to do…，被认为……，所以排除B,D；且主语Gunpowder和动词invent是动宾关系，所以要用不定式的被动形式，且invent发生在主句谓语动词believe之前，所以用不定式的被动完成时。选C。