At the meeting they discussed three different _________ to the study of mathematics.
If you won't do as I tell you, you ________ get the chance to be promoted because the competition is just too fierce.
We ________ have hurried all the way to the airport — the flight was called off because of the foggy weather.
—Mike, I can't find my watch anywhere.—You ________ it while working out.
—Where did you get this book?—I picked it up from a secondhand bookshop if you ________ know.
Jack is an outgoing child, usually kind and helpful, but he ________ lose temper sometimes.