There is no way of knowing why one man makes an important discovery ______ another man, also intelligent, fails.
Saving and recycling are long-term projects ____ determination matters a great deal.
You needn’t have come in person --- a letter _____enough.
--- What should I do with my paper, Mr. Jason? --- Well, what I have said about Peter’s _____ yours.
I heard that some patients who had undergone laser eye surgery experienced sudden losses of vision, ______?
--- I rang you at about ten, but there was no reply. --- Oh, that was probably _____ I was seeing the doctor.