The correct answer is A.
The conscription system, more commonly known as "the draft", is a mechanism that has been used by the US Federal Goverment to recruit civilians to become part of the US military forces in five different war conflicts:s: the American Revolution, the American Civil War, WWI, WWII, and the proxy wars included within the larger conflict known as Cold War (Korean War and Vietnam War).
All males between 18 and 25 had to be mandatorily registered and ready in case there is a war or national emergency and a draft is celebrated. Those who are called to serve cannot refuse.