By the middle of the 21st century, the vast majority of the world's population __________ in cities rather than in the country.
___ he did it remains a secret.
It was a pity that the great writer died _________his works unfinished.
That is not ____ I want.
In order to change attitudes _______ employing women, the government is bringing in new laws.
Please write me ____ you arrive in New York.