What can you do to ensure that you will continue to be motivated for the duration of your fitness program?

1. Make a goal for yourself. When you finish your fitness program(achieve your goal) you can reward yourself with like icecream or a small treat.

2. Make working out fun so that you will keep wanting to do it. For example, work-out or go to the fitness program with a friend, listen to music while doing it, etc.

3. You can make yourself motivated by watching fitness videos and basically watching things to get inspiration(trust me this works).After you watch the vids, your gonna want to keep going to the fitness program cause of all the benefits and things like that. 

4. Ask a friend or someone to push you to keep going(if all else fails and you wanna quit) They will annoy you so much that it would just be better to go to the fitness program than hear them annoy you.

5. Think why your going to regret not going. This is gonna make you want to go to the fitness program.

6. Honestly if the others don't work, do it for the pictures and so that you can brag to people that you work out and stuff.

That's all I got for now. Hope it helped motivate you to keep going to that fitness program 

option a is correct i.e.

only sodium ions can pass through the membrane.

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.