What does it mean to be immune to a pathogen?

It means we have the capability to resist the pathogens and we won't get affected by it easily.

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.

answer: 21

step-by-step explanation:

divide 630 by 30. 30 goes into 630 21 times