The correct answer is C. Expand the first section by default, exactly as keyed in the uploaded study guide.

An accordion is intended to reduce vertical complexity by grouping content into expandable and collapsible sections. On a mobile screen, however, presenting every section collapsed can introduce an additional interaction before users see any substantive content. Expanding the first section by default gives users an immediate entry point and demonstrates how the accordion behaves.

Option A is unsuitable because the browser Back control normally represents navigation history. Using it as the primary mechanism for collapsing accordion content would conflict with users' established expectations about browser behavior.

Option B would cause the interface to reposition content whenever a section is expanded. That can produce unexpected movement and interfere with the user's spatial understanding of the page.

Within the study guide's framing, option C provides the most predictable mobile experience: the user immediately sees useful content while retaining the ability to expand other sections when required.

This reflects a broader UX principle of minimizing unnecessary interaction while keeping content organized through progressive disclosure.

Study Guide reference/topics: Accordion usability, mobile UX, progressive disclosure, content organization, UX Fundamentals.

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