Many children were paralyzed by polio in the 1950s. Today, polio has been reduced by 99 percent. Which statement best explains how this disease has been almost eradicated?
A) Independent behavior helps humans live self-sufficiently and solve their own problems.
B) human communities use their ecosystems in creative ways.
C) human communities are learning to live with less money and fewer possessions.
D) Group behavior helps humans cooperate in order to accomplish large, complex tasks.
