An FAA Form 337 is used to record and document _____.

The FAA Form 337 is specifically used to record major repairs and major alterations on aircraft. These can include significant modifications or enhancements that affect the aircraft's structure, performance, or operational capabilities. This form not only documents the work performed but also provides a traceable history of modifications for regulatory compliance and safety assessments, which is crucial in aviation maintenance practices.

In the context of aviation regulations, it distinguishes between "major" and "minor" alterations and repairs, where major adjustments typically require more thorough documentation and inspection processes. The distinction is essential because major repairs or alterations often necessitate certain standards to ensure the continued airworthiness of the aircraft, which is a key focus of the FAA's oversight.

The other options incorrectly identify the scope of the form's use. Preventive maintenance and unscheduled maintenance are generally recorded separately and do not require a Form 337. Minor inspections, which involve routine checks that do not significantly alter the aircraft, also fall outside the need for such comprehensive documentation. Hence, the specific focus of the FAA Form 337 on major repairs and alterations makes option C the accurate choice.