Fill in the correct preposition.
e.g. Keep your mobile phones switched on at night.

16. If a burglar breaks into your house, always hand ... your valuables.

17. I ran ... an old friend at the supermarket yesterday.

18. We ran out ... milk, so can you buy some when you’re at the supermarket?
19. My brother and his friends hang ... at the shopping centre on Saturdays.
20. I saw two policemen running ... a robber.