National security is set up to do all of the following activities except:
a. defend against outside enemies
b. build the infrastructure of a nation
c. protect against subversive activities
d. assist in emergency situations

The correct answer is B. Build the infrastructure of a nation

Explanation:

The term "National Security" refers to different actions and organizations that guarantee the safety of a nation against different threats. In the U.S. the National Security refers to both the national defense and the relationship with other countries that guarantee the protection against any military or terrorist attack whether this originates in other country or within the U.S.; the protection of citizens in case of emergency situations as this represents a risk for national security; the use of armed forces if required and the implementation of multiple actions against terrorist or subversive activities that can represent a thread for society.

Therefore, it can be concluded the national security deals with multiple activities related to the safety of a nation except "Build the infrastructure of a nation" considering this is not directly related to safety and in consequence is not an issue related to the National Security.