The correct answer is option 2, which is the area planning approach.
Sectoral planning, option 1, refers to the approach of planning based on specific sectors or industries. This means that each sector or industry is planned individually, without considering the overall development of a particular area. This approach was not a special feature of the Sixth Five-Year Plan.
Option 3, planning for the top, does not provide any specific information about the special feature of the Sixth Five-Year Plan. Therefore, it can be eliminated as the correct answer.
Option 4, decentralization of the planning process, refers to the distribution of planning authority and responsibility to lower levels of government or local bodies. While decentralization may have been a part of the Sixth Five-Year Plan, it was not specifically mentioned as a special feature.
The special feature of the Sixth Five-Year Plan was the adoption of an area planning approach. This means that the plan focused on the overall development of specific geographical areas, taking into consideration the resources, infrastructure, and demographic characteristics of those areas. This approach aimed to ensure balanced development across different regions of the country.