Write the correct form of the verb in brackets: When we arrived, the film _______ (start).

The correct answer is 'had started'. Explanation: The sentence uses the past perfect tense because the action of the film starting happened before the action of arriving. 'When we arrived' is in the simple past tense. To indicate that the film started before we arrived, we need to use past perfect tense. Past perfect is formed by 'had' + past participle, so the correct form is 'had started'. Therefore, the complete sentence is: 'When we arrived, the film had started.'