This question directly tests knowledge of verb conjugations, specifically the past participle form. The past participle is 'eaten'. * **A is incorrect:** 'eating' is the present participle (used with continuous tenses). * **B is incorrect:** 'ate' is the simple past tense form of the verb. * **C is correct:** 'eaten' is the correct past participle form, often used with perfect tenses. * **D is incorrect:** 'eats' is the present tense third-person singular form. The core knowledge is understanding how past participles function and how irregular verbs are conjugated. **Core Concept:** Verb Conjugations, Past Participle **Solution Strategy:** Choose the past participle of the verb 'to eat'. **Option A Analysis:** 'eating' is the present participle, not the past participle. **Option B Analysis:** 'ate' is the simple past tense form, not the past participle. **Option C Analysis:** 'eaten' is the correct past participle form of the verb. **Option D Analysis:** 'eats' is the present tense, not the past participle. **Common Mistake:** Confusing the past participle with the simple past or other verb forms.