Complete the sentence with the verb in Present Perfect. Write down the correct form of the verb. A: Would you like something to eat? B: No, thanks. I _______ (just/have) lunch.

The sentence requires the Present Perfect tense. The structure is 'have/has' + past participle. The verb is 'have', and its past participle is 'had'. The sentence also includes 'just', which typically comes between the auxiliary verb and the past participle. Therefore, the correct form is 'have just had'.

Answer: have just had