Final answer:
The truth about lymph nodes is that they filter lymph through afferent vessels before it exits through efferent vessels and are filled with lymphocytes for purging infecting cells.
Step-by-step explanation:
The statement that is true about lymph nodes is: They filter lymph that enters the node through afferent vessels and leaves through efferent vessels; lymph nodes are filled with lymphocytes that purge infecting cells. This confirms that option b. "They have more efferent vessels than afferent vessels" is the correct answer. While lymph nodes may indeed swell in response to infection, they do not customarily reach the size of a golf ball, and they do not filter blood nor produce red blood cells. The primary functions of lymph nodes are to act as filters for foreign particles and cancer cells, and to participate in the immune response.