Ask the question that matters

Scenario

A founder says, 'Users love our product, so now we just need to scale marketing.'

Question

Which question is most useful to ask next?

1. A.What colors should the ads use?
2. B.What evidence shows users love it beyond a small enthusiastic group?
3. C.Which competitor spends the most on marketing?
4. D.Can the team work longer hours next month?