Derive an expression for the equivalent capacitance of series combinations .

Question

$\begin{array}{1 1} (a)\; \large\frac{1}{c}=\frac{1}{c_1}+\frac{1}{c_2}+\frac{1}{c_3} \\ (b)\;C=c_1+c_2+c_3\\ (c) C=\large\frac{1}{c_1}+\frac{1}{c_2}+\frac{1}{c_3} \\ (d) C=\large\frac{1}{c_1+c_2+c_3}\end{array} $