She gives several reasons why people need to make changes to their eating habits and exercise routines
If you start doing it more will follow, so as the pigs lead the animals follow whatever they say even if it doesn’t seem right or the rules seem to keep changing they don’t question it because the other ones are doing it
Even though you didn't give us the fragment with the comma slice, it isn't really necessary here as we can answer just based on these 4 options here. All options apart from the second one are correct - only the second option doesn't fix the mistake of the comma splice, whereas the other options do but connecting the sentences properly.
I believe b, because then is considered a transition word
