Correct Answer & Explanation
Option C
• This sentence describes two past actions: 'finishing shopping' and 'it started raining'.
• According to the rules of Past Perfect Tense, when two actions happened in the past, the action that occurred earlier is expressed in the Past Perfect Tense (had + V3), and the later action is in the Simple Past Tense (V2).
• In this case, 'finishing shopping' happened before 'it started raining'.
• Therefore, 'had finished' is the correct form for the earlier action.