The Cuyahoga River actually caught on fire in the 70s because it was so polluted. Many people in the past (prior to the 1980s) did not understand that:

Earth's resources are unlimited.

We can get resources from the Earth as well as other planets.

Doing something to one sphere of the Earth effects the other spheres.

The Earth's can provide everything we need no matter what we do to it.

In the past, most people would think that our planet could provide us with anything, whatever we did to it. They thought so because the Earth seemed so vast and rich. However, they were wrong. Most resources like water and petroleum or gas are limited and others like forestry take a long time to generate. After the industrial revolution, man had a lasting negative effect on nature. The correct answer is c. The people there could not understand that polluting the soil or the area around the river would influence the river itself. In the older days, effects like pollution were diluted and because the effects were not seen in the same place, many people did not bother about them. But out pollution affects some place in the Earth, it does not go away. The systems in the Earth are intricately connected between them and this refers to pollution too.