For logarithm of time fitting method, the coefficient of consolidation is detained from ________

• A. \(c_v=\frac{(T_v)_{70} d^3}{t_{70}} \)
• B. \(c_v=\frac{(T_v)_{80} d^2}{t_{80}} \)
• C. \(c_v=\frac{(T_v)_{90} d^4}{t_{90}} \)
• D. \(c_v=\frac{(T_v)_{50} d^2}{t_{50}} \)