Concept:Evolutionary advancement in animals is judged by increasing structural complexity and specialization.
Explanation:Liverfluke is a flatworm with a very simple body plan.
Earthworm is an annelid, showing segmentation but still relatively simple.
Snail is a mollusc, more advanced but less specialised than arthropods.
Cockroach is an arthropod, possessing jointed appendages, a well-developed nervous system, and advanced body organisation.
Among the options, cockroach has the most advanced evolutionary features.
Answer:D. Cockroach