The function of the lymph nodes is to:

The primary function of the lymph nodes is to purify the lymphatic fluid by filtering out harmful substances, such as pathogens and debris. Lymph nodes are an integral part of the immune system, helping to identify and destroy invaders like bacteria and viruses. When lymph fluid flows through the nodes, it encounters lymphocytes—specific types of white blood cells that play a vital role in the immune response. This filtering process ensures that the lymph is cleansed and that any harmful substances are dealt with before the lymph returns to the bloodstream.

While lymphocytes are indeed produced within lymph nodes, the filtering function highlights the lymphatic system's role in protecting the body from infection and disease. This makes the function of purifying the lymph the most accurate description of what lymph nodes do. In comparison, the other choices either pertain to functions primarily associated with different systems in the body or do not highlight the key role played by the lymph nodes in immune defense.