Three capacitors each of $4 \mu F$ are to be connected in such a way that the effective capacitance is $6 \mu F$. This can be done by connecting them :

Question

$\begin{array}{1 1}\text{(1) all in series} \\ \text{(2) two in series and one in parallel} \\ \text{(3) all in parallel} \\ \text{(4) two in parallel and one in series} \end{array}$