The primary role of the lymphatic system is to maintain fluid balance and support immune function. It plays a critical role in returning excess interstitial fluid, which is the fluid that surrounds cells, back to the bloodstream, thereby preventing tissue swelling and maintaining normal blood volume.
Additionally, the lymphatic system is integral to the immune response. It facilitates the transport of lymph, which contains white blood cells, particularly lymphocytes, that are crucial for the body's defense against infections and diseases. This system also helps in filtering pathogens and foreign substances through lymph nodes, which are strategically located throughout the body.
The other options do not accurately represent the role of the lymphatic system. For example, transporting oxygen is primarily the function of the circulatory system, digestion is managed by the gastrointestinal system, and body temperature regulation is primarily controlled through processes involving the skin and the endocrine system. Thus, the correct answer emphasizes the dual function of fluid balance and immune support that is characteristic of the lymphatic system.