How does a compression test help distinguish between mechanical problems and valve leakage as the cause of low compression?

How does a compression test help distinguish between mechanical problems and valve leakage as the cause of low compression?

• A. A dry compression test shows cylinder pressure; many low readings point to mechanical issues. A single low reading suggests valve leakage or seating problems; a wet test showing significant rise indicates worn rings.
• B. A dry compression test measures fuel pressure in the rail; it cannot indicate valve leakage.
• C. A dry compression test will always show equal pressure in all cylinders.
• D. A dry compression test measures coolant pressure in the cylinder head.

Answer: (A)