Step 1: Identify the time reference point. "By the time the results were announced" sets a past reference point. The action of preparing happened BEFORE this past point. Step 2: Determine aspect. "For three gruelling months" signals duration — the action was ongoing over a period. Duration signals continuous aspect. Step 3: Combine tense and aspect. Past time before another past point = past perfect. Ongoing duration = continuous. Together: past perfect continuous = "had been preparing". Step 4: Reject alternatives. "Has been preparing" = present perfect continuous (wrong tense anchor). "Was preparing" = past continuous (no 'before another past point' meaning). "Had prepared" = past perfect simple (loses duration). Answer: "had been preparing"