Final answer:
Events B) The Organization of American States (OAS) was formed, and D) The formation of the Southeast Asia Treaty Organization (SEATO) occurred during the Cold War era.
Step-by-step explanation:
The Cold War era was a period of geopolitical tension between the United States and the Soviet Union, and it included several significant events. Among the options provided, the event that occurred during the Cold War era was B) The Organization of American States (OAS) was formed. The OAS was established in 1948 with the aim of promoting regional solidarity and cooperation among countries in the Americas. Additionally, D) The formation of the Southeast Asia Treaty Organization (SEATO) also took place during the Cold War, in 1954, as part of the U.S. strategy to prevent the spread of communism in Southeast Asia.
While the Limited Test Ban Treaty was indeed signed by the United States, Great Britain, and the Soviet Union during the Cold War in 1963, it is not one of the available answers.