Answer: a. By rewriting the archives of the London Times, he makes them consistent with current Ingsoc.
Explanation: Big Brother and The Party must always be right, so if he said something in the past that does not correspond with current reality, the previous statements are altered to make it appear that Big Brother knew what would happen. There is no accurate record of previous events or statements that might prove that the Party has made mistakes, or that current conditions are worse than they were in previous times.