As "civilization" spread around the world, several species benefitted greatly from new human-made habitats, including the house fly, the Norwegian rat, and many crop plants. Generally, with expansion of human populations and agriculture,
A. there has been an increase in biological diversity.
B. biological diversity has remained the same, with human-associated organisms replacing the few natural species displaced.
C. biological diversity has decreased but mainly with the elimination of pests by humans.
D. biological diversity is decreasing at an accelerating rate with the elimination of many unstudied species.