One example of animals having a single opening to the outside that serves both as mouth as well as anus is (a) Octopus (b) Asterias (c) Ascidia (d) Fasciola.
Option D In Fasciola (flatworms) the body has a single cavity with one opening to the outside. The single opening functions as both mouth for ingestion (intake of food) and anus for egestion (undigested food is passed out). It is called blind sac plan. Other examples are coelenterates.
