A comparison question can still be useful when some requirements are unknown. Name the options, the job they need to do, and the criteria you can already judge: cost, setup effort, privacy, compatibility, or maintenance. Mark unknown constraints instead of filling them with assumptions.
For example: “I need to share a report with five editors. Option A supports offline work; I have not confirmed whether option B permits external guests.” Ask which missing fact is most likely to change the recommendation. Include your current preference only as a hypothesis. A good answer should be able to explain both when each option wins and what evidence would settle the undecided case.
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