The correct answer is A. Mean Time to Repair . Designing for maintainability means designing assets so they can be inspected, serviced, repaired, restored, and returned to operation quickly, safely, and consistently. MTTR is the most direct measure because it reflects how long restoration typically takes after failure. Design features that reduce MTTR include good access, modular replacement, standardized parts, clear isolation points, lifting points, diagnostics, labeling, safe work access, and simplified disassembly. Total cost of ownership is important in asset management, but it is broader than maintainability and includes capital, energy, maintenance, downtime, spares, disposal, and other lifecycle costs. Component availability may support maintainability if parts are available, but it is not the main maintainability design measure. In CRL Reliability Engineering for Maintenance, maintainability is a design and strategy concern because hard-to-maintain assets increase downtime, labor cost, safety exposure, and poor work quality. MTTR is widely defined as the average time required to repair or restore equipment after failure.