The correct option is B Oligotrophic soil
Oligotrophic soils are poor in nutrients. One such type of soil which supports dense vegetation is the one found in tropical rain forests. Here the top soil is shallow while subsoil has dense clay mixed with iron-aluminium compounds. Despite growing in oligotrophic soil, nutrient accumulation is high in vegetation. A major adaptation of tropical plants is present of mycorrhizae. Mycorrhiza is a mutualistic association of plant roots with fungi, It is useful in the retrieval of critical elements from organic compounds e.g., phosphorous, absorption of water and protection from soil borne pathogenic fungi.