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} )