What are subgrade and base layering in pavement design?

What are subgrade and base layering in pavement design?

• A. Subgrade is the prepared soil supporting the pavement; base layer provides structural support and drainage; both require compaction.
• B. Subgrade is asphalt; base is concrete; no compaction needed.
• C. Subgrade is the topsoil; base is landscaping gravel; both un-compacted.
• D. Subgrade is drainage layer; base is reinforcement fabric.

Answer: (A)