The core concept is understanding past perfect tense, which is 'had + past participle'. The past perfect tense is used to describe an action that was completed before another action in the past. - **Correct Answer:** C. 'I had finished my work by the time he arrived' correctly uses the past perfect tense to indicate finishing work before arrival. - **Incorrect Options:** - A. 'She had eat dinner' is incorrect because 'eat' should be the past participle 'eaten'. - B. 'They has gone' is incorrect as 'has' is singular. It should be 'had gone'. - D. 'He have seen' is incorrect as 'have' is used with plural. It should be 'had seen'. **Core Concept:** Past Perfect Tense **Solution Analysis:** The question tests the formation of past perfect tense. The correct option follows the 'had + past participle' rule. **Detailed Analysis:** - Option A: Incorrect, uses the base form of the verb 'eat' instead of 'eaten'. - Option B: Incorrect, uses the singular form of the helping verb 'has', should be 'had'. - Option C: Correct, uses the helping verb 'had' correctly with past participle 'finished'. - Option D: Incorrect, uses the wrong helping verb, should be 'had'. **Common Mistake:** Confusing the helping verbs or using the base verb form instead of the past participle.