For the first question, the answer would be B. Low genetic diversity causes a species to have a likely chance of becoming extinct should a natural disaster hit. For example, birds and the dinosaurs. Birds are descendants of dinosaurs and survived the Ice Age by having a means for keeping warm, while the bigger reptiles died out due to genetic diversity not making them as adaptable. That's why the lizards today are smaller, because their size (less food needed to survive, and kept warm with smaller amounts of sunlight) allowed them to survive and reproduce.
As for the second question, the answer would also be B. Diversity has become greater over time. An excellent example are the Galapagos island finches. Due to natural disasters, the species have been divided up and thus adapted different wingspans and beak shape to fit their diet over generations.