What is the primary function of the circulatory system

To allow efficient distribution of materials within the body

Explanation:

Circulatory system in mammals especially human provides an efficient way of distribution of materials within the body.

This is made possible by blood and lymph which represent the media for circulation in humans

option a is correct i.e.

explanation:

in context to the membrane of nerve impulse, the outer membrane of neuron is semi permeable that is only sodium ions can pass through the membrane i.e. smaller ions can pass through the membrane while larger ions cannot pass through it.