The common difference of the A.P. 12b, 1 - 6b2b, 1 - 12b2b, . . . . . is

Answer: Option D

$$\begin{array}{rl}& A.P.is\frac{1}{2b},\frac{1-6b}{2b},\frac{1-12b}{2b},....\\ & \Rightarrow \frac{1}{2b},\frac{1}{2b}-\frac{6b}{2b},\frac{1}{2b}-\frac{12b}{2b},....\\ & \Rightarrow \frac{1}{2b},\frac{1}{2b}-3,\frac{1}{2b}-6,....\\ & \therefore d=\frac{1}{2b}-3-\frac{1}{2b}=-3\end{array}$$