The correct answer is option 1: Leucocytes. Leucocytes, also known as white blood cells, play a vital role in building up resistance against diseases in the body. These blood corpuscles are involved in the immune response of the body and help fight against harmful pathogens, such as bacteria, viruses, and fungi.

Leucocytes are produced in the bone marrow and can be categorized into different types based on their functions and characteristics. One of the main types of leucocytes is lymphocytes, which are responsible for the production of antibodies that target specific pathogens. Lymphocytes are further divided into B cells and T cells, each playing a specific role in the immune system.

Monocytes, neutrophils, and lymphocytes are all types of leucocytes, but in this particular question, the correct answer is leucocytes in general. It is important to note that while all leucocytes contribute to building resistance against diseases, they may have different functions within the immune system.

Alert - correct answer should be lymphocytes