Question

--- Who ________ paper in the world?

--- Cai Lun ________.

1. A.
   invented; did
2. B.
   was invented; was
3. C.
   did invent; was
4. D.
   invented; was

Answer 1

A
who是动作的发出者，用主动语态invented。下句使用did来替代invented。