What is the mathematical expression of BOD?

• A. tBOD = [(D1-D2)-(B1-B2)f]/P
• B. tBOD = [(D1-D2)-(B1-B2)f].
• C. tBOD = [(D1-D2) f]/P
• D. tBOD = [(D1-D2)-(B1-B2)]/P