Nehruvian Planning, the economic approach adopted by Jawaharlal Nehru, emphasized the growth and development of heavy and core industries. This means that the focus was on establishing and expanding industries that were essential for the overall industrial development of the country.

Option 1, agriculture through modern technology, does not align with the emphasis of Nehruvian Planning. While agriculture and modern technology were indeed important, they were not the central focus of this economic approach.

Option 2, science and technology, also does not accurately represent the main emphasis of Nehruvian Planning. Although Nehru did recognize the significance of science and technology in the country`s development, it was not the primary area of focus.

Option 4, small-scale industries, is another incorrect option. While small-scale industries did play a role in Nehruvian Planning, they were not prioritized as heavily as heavy and core industries.

Therefore, the correct answer is option 3, heavy and core industries. This answer aligns with the primary objective of Nehruvian Planning, which was to promote industrialization and build a strong industrial base in India.