The formula of API degree is _______

• A. \(\frac{141.5}{specific\, gravity \,of \,oil\, at\, 60℉}\) – 13.15
• B. Specific gravity of oil-13.5
• C. \(\frac{141.5}{specific\, gravity \,of\, oil}\)+131.5
• D. \(\frac{specifc gravity of oil+41.31}{141.5} \)