Personally I would say the true answer is b as I believe the population of humans is quickly overwhelming the environment. This world cannot support 7 billion people especially if they want all the modern things such as cars, planes, electricity, and food. We are causing massive carbon dioxide build up in the atmosphere which is acidifying the oceans and will eventually kill most sea life. This will be a catastrophe for countries like Japan who get most of their protein from fish. The carbon dioxide will also cause extreme glass house type heat causing massive droughts, ice and snow melts, seas to expand, and about half our land mass to disappear under water.
Man cannot just switch off all his polluting as without electricity people will revert to cooking over fires and that will cause more pollution than coal powered power stations. City people could be forced onto upgraded public transport and most could stop driving cars but the fact is most won't do it. High flying Jet aircraft do destroy ozone which is one of the main things protecting us from severe ultraviolet rays from the sun, and cars are pouring out carbon dioxide at an alarming rate.
Asia is modernising demanding the right to have the luxury and waste of the western world and are polluting on an industrial scale and are not going to say ok we will go back to our old peasant ways so you westerners can keep polluting. I believe it is already too late and the human race is going to suffer badly in the next century or so. The world is already showing signs that it is being overwhelmed by the pollution of mankind.