I think what's common between the three is that, these are the turning points where human minds brought about change out of necessity. The ages before those mentioned are periods of great depressions and unfortunate event. So, these fueled the people to change for the better and appreciate science and art more.
Training people to fight the Cubans.
Answer: B
Explanation: Stem cells are the building blocks of the human body. At the start of life, they divide over and over again to create a full person from an embryo. As we age, they replenish cells in our blood, bone, skin and organs. Stem cells could be powerful tools in treating injury and illness.
