During the transmission of nerve impulses through a nerve fibre, the potential on the inner side of the plasma membrane has which type of electrical charge?

Question

$\begin{array}{1 1} \text{a. First positive, then negative and continue to be negative} \\ \text{b. First negative, then positive and again negative} \\ \text{c. First positive, then negative and again back to positive} \\ \text{d. First negative, then positive and continue to be positive.} \end{array}$