—Where did you get this book?—I picked it up from a second-hand bookshop if you ______know.
The old man stood there with his eyes ______ on the picture.
Scientists are convinced ______ the positive effect of laughter ______ physical and mental health.
---I’m going out tonight. ---Well, I’d rather you ______.
Bitten twice, the postman refused to ______ our letters unless we changed our dog.
______ to go abroad alone is what worries me most.