C. Have fooled (that's the correct answer)
C) have fooled "Oh, you 'have fooled' us twice," they said. "You shall not have another chance."
The correct answer is C) have fooled, which utilizes the present perfect tense to indicate a past action relevant to the present. The structure 'have + past participle' is needed here, making it the only grammatically correct choice. The other options either misuse verb forms or are informal and incorrect in this context.
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