Let’s examine the sentence: “You say you have gone to his office, but I think you ____” The sentence blank in the sentence requires a clause that is in line with the clause, ‘you have gone to his office,’ as both are stating something about the same event occurring in the same time. Now, since the given clause is in present perfect tense containing ‘have’ as a helping verb, the clause required to fill in the blank should also fulfill this condition. Options A, C and D cannot be used as they do not contain the helping verb ‘have’ and their usage would make the sentence grammatically incorrect. Hence, Option B is the correct answer.