问题补充:
Gunpowder is generally believed in ancient China.
A. to have invented
B. being invented
C. to have been invented
D. having invented
答案:
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。