Answer:
Vaccines take a long time to develop and make.
Explanation:
The cure (vaccines) to problems like smallpox take a while to develop as scientists and doctors need to make it correctly and test it correctly to see if it is a cure or not. It takes years before these things can be distributed and/or even verified for "it works!" Due to this, it may of took a century for development, planning, making, testing, getting approved and mass distributing.
B. In order of increasing atomic Mass :)
Usually, when mutations cause major changes in the external appearance of a population, the selection mode is how well that new color blends in with its environment. It it blends well, the animal will be hidden better from predators and survive.