Change from Active to Passive Voice: "She was watching a film."

A film is being watched by her

A film will be watched by her

A film was being watched by her

None of these

Active Voice: She was watching a film. (The subject "she" is performing the action)

Passive Voice: A film was being watched by her. (The subject "a film" is receiving the action)

In the passive voice, the focus is on the object (the film) rather than the subject (she).