Which fluid contains white blood cells and drains through the lymphatic system?

Lymph is the correct answer because it is a clear fluid that contains white blood cells, primarily lymphocytes, which play a crucial role in the immune system. Lymph circulates through the lymphatic system, a network that helps to remove waste and toxins from bodily tissues while also transporting lymphocytes to areas of infection or inflammation.

In contrast, serum and plasma are components of blood. Plasma is the liquid part of blood that carries blood cells, nutrients, and hormones, while serum is the fluid that remains after blood has clotted and does not contain clotting factors. Synovial fluid is a viscous fluid found in the cavities of synovial joints that helps reduce friction between the articular cartilage of synovial joints during movement and provides cushioning, but it is not involved in the lymphatic drainage system. Therefore, lymph is specifically the fluid that contains white blood cells and drains through the lymphatic system.