Answer:
B. serving in the military
Explanation:
It is a legal and ethical obligation for US citizens to serve in the military whenever necessary. Military enlistment of male US citizens occurs at 18; of male immigrants, between 18 and 25 years old. But mandatory enlistment has not been in place since the Vietnam War, and the United States Army is currently an entirely voluntary force, but it is the duty of all citizens to serve in the armed forces at the moment they are called.
