The correct answer is Option 1, i.e Containment of Communism.
The main objective of the Truman Doctrine was the containment of Communism which was proposed by the then US President Harry S. Truman in the era of Cold war.
Harry S. Truman established that the United States would provide political, military and economic assistance to all democratic nations under threat from external or internal authoritarian forces.
In 1947, President Harry S. Truman pledged that the United States would help any nation resist communism in order to prevent its spread and provided 13 billion of aid to Europe in the Marshall Plan.
In the light of the Truman Policy, the US along with its allies helped South Korea in the war against North Korea where North Korea was backed upon by USSR and PRC.