How long do you think it will be _____China becomes a developed country?—At least 20 years, I guess.

He made another wonderful discovery, ______ of great importance to science

John was late for the business meetingbecause his flight had been _______ by a heavy storm.

If you see the cartoon film, you’ll laugh.

Have you been to Australia?—Yes, only onceI ____ there only for seven days[ ]