_____ human beings live in great numbers, the waters are very likely to become contaminated.
The news _____ he has passed the exam makes his parents very happy.
It was not until he became very ill ______ he went to see a doctor.
______ from the moon, the earth looks like a beautiful blue planet.
___we do this today or tomorrow doesn’t make much difference.
—Do you think I should wear a thick coat? —Yes, certainly. ______, you also need a compass.