Which sentence has the most appropriate tone for persuading people to recycle?

a. if we don’t start recycling immediately, our grandchildren will have to live in a very bleak world.

b. thoughtless, inconsiderate people who refuse to recycle are just wasting natural resources.

c. if we recycle, we are using natural resources more responsibly for the sake of future generations.

d. everybody has to see that recycling has lots of good points and would make such a big difference.