Mr. Smith graduated from college at the age of 23, and ___________ he has been working as a teacher in a middle school.
--- The conflict between North and South Korea calls for talks to solve the problem.---Quite right. I would rather the UN_______ something immediately.
With such an ecological variety, amazing natural beauty, and so much to do, it's _______ that the falls are a wonder.
Having finished the work, _______.
---When was Tom bitten by a snake?---It was on a Sunday _______ he was taking a trip to the mountainous area.
When this new kind of virus broke out at first in Mexico, no one had the least idea that it would _______ so rapidly throughout the world.