What structures act as filters to trap pathogens and damaged cells as lymph flows through them?

Spleen

Explanation:

The is because the spleen is an organ found in upper section of the abdomen spleen acts as a filterand it help to remove old and damaged cells . It also play a major role in controlling the amount of blood and blood cells that move round the body. The spleen also helps remove pathogens. It contains white blood cells called lymphocytes and macrophages.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.