The correct answer is option 3: Using high-yielding varieties (HYV) seeds. After Independence, the Government of India implemented several strategies to increase food grain production in the country. Let`s explore each option to better understand the correct answer.

Option 1: Intensification of cropping over already cultivated land. This strategy involved promoting multiple cropping cycles within a year by utilizing the same parcel of land more efficiently. It aimed to maximize crop yield and increase overall production.

Option 2: Increasing cultivable area by bringing cultivable and fallow land under the plough. This strategy focused on identifying and utilizing unused or uncultivated land for agriculture. By bringing more land under cultivation, the government aimed to increase the total area available for agricultural production.

Option 3: Using high-yielding varieties (HYV) seeds. This option is not a part of the strategies implemented by the government to increase food grain production. However, HYV seeds were indeed introduced in India as part of the Green Revolution in the 1960s, which aimed to enhance agricultural productivity.

Option 4: Switching over from cash crops to food crops. This strategy involved promoting the cultivation of food crops, such as rice and wheat, instead of cash crops like jute or cotton.