What is a primary responsibility of the department of defense?
a. to formulate diplomatic policy
b. to implement military policy
c. to coordinate domestic security efforts
d. to advise the president about national security threats?

The primary responsibility of the department of defense is to implement military policy. Their mission is to provide military forces needed to deter war and protect the security of the country. Under their primary responsibility are preparation of military strategy, preserving armed forces, operational military bases around the world and protecting the countries from foreign terrorizations. The president is a civilian and he is over the armed forces, each branch is headed by a secretary that is civilian which is the secretary of defense and deputy secretary of defense. They constitute the immediate military staff of the department of defense. The joint of staff are composed of the senior military officers of certain services. 

Idon't understand ur ?