Choosing the Right Prototype for a Usability Test

You need to usability-test a new multi-step filter-and-search flow for an e-commerce app before committing engineering time to build it. You have two prototype options ready by the deadline:

• Option A: a single, beautifully polished static image of the final filter screen, matching the intended shipped visual design exactly.
• Option B: a grayscale, unstyled version of the full flow with every screen actually clickable — filters can be applied, results update (with placeholder data), and users can navigate all the way through to a result.

1. Which option should you use for the usability test, and why, using the fidelity-vs-interactivity distinction from this subject?
2. What specific failure would Option A produce if you tried to run the test with it anyway?
3. What's the risk, if any, of using Option B instead of Option A — what won't this test tell you that a higher-fidelity test would?