Option C, "Necessary and Proper" clause, is the right answer.
Explanation:
In the Constitution of the United States, the Necessary and Proper Clause is a clause found in Article I of section VIII. This clause is also known as the Elastic Clause of the U.S. Constitution. The Necessary and Proper Clause enables the Congress of the United States to make all laws required and proper for the Execution of all the Powers along with the Enumerated powers. This clause was added to the U.S Constitution to maintain the commitment to "strict construction" of federal powers.
It was primarily the "b. formation of the Vietcong in Vietnam" that led the Truman administration to expand the containment doctrine to include Asia, since this was seen as a threat to democratic principles in the west as well.
