The characteristic equation of an SR flip-flop is given by

A

$$Q_{n + 1} = S + RQ_{n}$$

B

$$Q_{n + 1} = R \overline{Q}_n + \overline{S}Q_n$$

C

$$Q_{n + 1} = \overline{S} + RQ_n$$

D

$$Q_{n+1} = S + \overline{R} Q_{n}$$