Final answer:
The lymphatic system assists blood flow by draining excess fluid and returning it to the bloodstream, eventually reducing the interstitial fluid accumulation and maintaining fluid balance.
Step-by-step explanation:
The lymphatic system works with blood flow by draining excess interstitial fluid from tissue spaces and returning it to the bloodstream. This maintains fluid balance within the body and facilitates the removal of pathogens and cellular debris. The excess fluid, now called lymph, collects in lymphatic vessels and is filtered through lymph nodes where it is cleansed of impurities and immune responses can be mounted. The cleaned lymph eventually drains back into the bloodstream at the upper chest area. Moreover, the lymphatic system transports dietary lipids absorbed from the small intestine and houses lymphocytes, key cells involved in the adaptive immune response.
Answer A, 'Drains excess fluid and returns it to blood vessels,' accurately describes a major function of the lymphatic system in relation to blood flow.