Hydroelectric energy uses the movement of water to spin a turbine and produce electricity. Coal is a fossil fuel that is burned as an energy source, which results in emissions such as carbon dioxide, nitrogen, and sulfur. Coal use is associated with waste products both from the mining process to acquire the coal and also from the actual use of coal itself. Hydroelectric energy does not involve waste, but does pose potential problems to waterways. Coal use is more common than the use of hydroelectric energy.<span> </span>
The best option from the list would be that "<span>b. The United States began to build up its military and to stockpile weapons," since this was part of the inevitable "Arms Race" that took place between the US and the USSR. </span>
Due to geopolitical reasons, most of emigration out of Africa and Middle East have been to the Western Hemisphere; instead of the East. Adding the original native Americans in the Americas, the Western Hemisphere is currently much more diverse than the East.