East and South Asia form a region due to some the similarities like ancient civilizations, Asian isolationism, climate, and religious belief system.
Options A, B, and C are the correct answers.
Isolationism refers to the practice followed whereby countries have abstained from the formation of alliances and involvement in political and economic relations globally.
Both the regions have their respective similarities due to which they are treated like one region. The climatic effects are very much common in these regions, they have gone through isolationism for about thousands of years, a maximum of civilizations in an ancient era emerged in these regions and the people also have alike beliefs about their religions.
Therefore, apart from the explanation given in option D, all the options described the similarities between East and South Asia.
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