A courier service outlet saw complaints rise by 40% this month compared to last month, concentrated on delivery delays. The manager precisely defined the outcome, listed three possible causes—insufficient staff, route adjustments, and weather impacts—and drew a cause chain. He then decided to trial a new scheduling plan in one adjacent district next month while leaving other districts unchanged. According to the six-step causal analysis method, which step is still missing before he makes this decision?

Answer: A

• AGathering supporting and opposing evidence for each hypothesis, such as insufficient staffing and route adjustments.✓ Correct. After listing causes and before testing, evidence should be gathered for each hypothesis; for example, if insufficient staffing is true, delays should concentrate during the least-staffed periods. Missing this step turns the trial into a blind bet on untested assumptions.
• BRewriting "increase in complaints" into a precise statement specifying the object, time, and extent.✗ Incorrect. The stem clearly states that the manager has already precisely defined the outcome, so this step is complete—this option reflects a failure to see where the process currently stands.
• CListing more possible causes from additional dimensions to make the cause list more comprehensive.✗ Incorrect. The three causes already cover personnel, process, and environment, meeting the 'at least three' requirement; adding more causes does not replace evidence testing of existing hypotheses, corresponding to the misconception that 'the more complete the list, the better.'
• DAfter the trial ends, if complaints decrease, reviewing to exclude new factors and check implementation fidelity.✗ Incorrect. Review is the sixth step, which occurs after the trial; using it to replace pre-decision evidence testing reflects a reversal of order, 'acting first and explaining after getting results.'