Use the right forms to complete the sentences when i was in great britain, i often (understand) what english people were saying. i know bob (understand) my question yesterday they dont (understand) italian. do you think tom (understand) what he is doing

When I was in Great Britain, I often (understood) what English people were saying.
I know Bob (understood) my question yesterday.
They don't (understand) Italian.
Do you think Tom (understands) what he is doing.