A is definitely the best answer. Renewable resources are things like sunlight, wind, or tidal energy, which replace themselves without any human help.
B is wrong because renewable resources can definitely be harmed by humans. Sunlight can be blocked by pollution, for instance, and tides can be harmed by things like dams or erosion.
C is wrong because most of our energy comes from no renewable resources like fossil fuels (oil, coal, gasoline).
D is wrong because renewable resources can sometimes (but not all the time) be quite expensive to use. Hydroelectric energy requires extremely expensive dams, for instance, though wind power can sometimes be relatively inexpensive.
