The answer is A. movement of energy through space or a medium
Balance
It is the tendency of the social system, when disturbed, to return to its original state. This is because change in one element is often accompanied by changes in other related elements.
The first mask was made in 7000 BC. It was used primarily for rituals and ceremonies and where typically made of leather or wood. Keep in mind, these where the first masks that our modern generation has been able to find and preserve, masks could have been made earlier than this but detirriorated over time.
However, the first modern surgical masks where made in the early 1960s and replaced a more primitive method of cloth masks.
I hope I have helped! :)
Each country had a different economic system (capitalism in the USA and communism in the SU), which caused competition.
This competition led to military competition and a nuclear arms race, which was called the Cold War. The nuclear arms race became the greatest point of tension.
