(1) An action in the past that is often of a temporary nature.
(2) An action in the past that acts as a background or an action that is interrupted.
(1) When she was living in London, she worked as an interpreter for six months.
(2) While he was eating his dinner last night, he heard the sound of a loud explosion in the street
Both sentences are positive. In order to make them negative we have to change them as (1) I wasn't (was not) living (2) he wasn't (was not) eating.
Both sentences are statements. In order to make them interrogative we have to change them as: (1) was she living? (2) was he eating?
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