The correct answer is B) transitional ecosystem. An ecotone is defined as a transition zone between two different ecological communities or ecosystems. It contains species characteristic of both bordering ecosystems, and often includes species not found in either. Ecotones are important ecologically as they often have higher biodiversity (edge effect) than the adjacent ecosystems due to the presence of species from both communities. Examples include the transition between a forest and a grassland, or a riverbank bordering a terrestrial area.