During development of action potential in a nerve fibre, positive and negative charges on outer and inner side of axon membrane are reversed due to
A. Excretion of all `K^(+)` ions
B. More `K^(+)` ions enter than `Na^(+)` ions leave the axon
C. More `Na^(+)` ions enter the axon than `K^(+)` ions have leave the same
D. All `Na^(+)` ions enter the axon