The correct answer is option 'B' - Improve resistance to diseases.

Biofortification is a process that aims to improve the nutritional quality of crops by increasing the content of essential vitamins, minerals, and other nutrients. It is an effective strategy to address malnutrition and micronutrient deficiencies in populations that heavily rely on staple crops for their daily diet. While the primary objective of biofortification is to improve the nutritional value of crops, it does not directly focus on improving resistance to diseases. Here's an explanation of the other objectives of biofortification:

a) Improve protein content:
- Protein is an essential macronutrient required for growth and development, and insufficient protein intake can lead to malnutrition.
- Biofortification aims to improve the protein content of crops to provide a more balanced and nutritious diet for communities.

c) Improve vitamin content:
- Vitamins are essential micronutrients that play crucial roles in various physiological processes.
- Biofortification focuses on increasing the content of vitamins such as vitamin A, vitamin C, and folate in crops.
- Vitamin A deficiency is a significant public health problem in many developing countries, leading to impaired vision and increased susceptibility to infections.
- By biofortifying staple crops with vitamin A, it is possible to enhance the nutritional status of populations and reduce the incidence of vitamin A deficiency-related health issues.

d) Improve micronutrient and mineral content:
- Biofortification also aims to increase the content of other essential minerals and micronutrients in crops, such as iron, zinc, and iodine.
- Iron and zinc deficiencies are widespread globally and can lead to impaired cognitive development, weakened immune systems, and increased risk of diseases.
- By biofortifying crops with iron and zinc, it is possible to improve the nutritional status and overall health of populations.

In summary, while biofortification has several objectives, such as improving protein content, increasing vitamin content, and enhancing micronutrient and mineral content, it does not directly focus on improving resistance to diseases. However, by improving the nutritional quality of crops, biofortification indirectly contributes to strengthening immune systems and reducing the risk of disease in populations.