- Regional analysis- Later Colonial period(This approach has historical roots and was a fundamental approach in early human geography.)
- Areal differentiation- 1930s through the inter-War period(Areal differentiation, which involves the study of spatial variations, often developed alongside regional analysis.)
- Emergence of radical school- 1970s(The radical school, also known as Marxist geography, emerged as a critical perspective in human geography later.)
- Post-modernism in geography- 1990s(Post-modernism in geography is a more recent development in the field, emerging in the latter part of the 20th century.)
Therefore, the correct answer is option 4: B, D, A, C.