---Inventors have changed the way we live.

---So they are famous for the great things they ________.

1. A.
   do
2. B.
   did
3. C.
   are doing
4. D.
   had done

—Inventors have changed the way we live.

—So they are famous for the great things they ___.

A. do                B. have done        C. are doing              D. had done