Correct Answer & Explanation
Option C
• This sentence describes two past actions: 'arrived' and 'the train leaving'.
• When two actions occur in the past, the one that happened earlier is expressed in the Past Perfect Tense, and the later action in the Simple Past Tense.
• The train leaving happened before I arrived.
• The structure for Past Perfect Tense is Subject + had + V3 (past participle).
• Therefore, 'had left' is the correct form to indicate the action that occurred first.