1. The most important thing about cotton in history is ___part that it played in ___Industrial Revolution.
A. ∕；∕ B. the；∕ C. the; the D. a; the
2. It was a time_______ the killer whales helped the whalers catch the baleen whales.
A. when B. that C. then D. which
3. Robert is said ____ abroad, but I don’t know what country he studied in.
A. to have studied B. to study C. to be studying D. to have been studying
