The correct option is
B Mycelium
Mycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called as shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelium are found in and on soil and many other substrates.
Thallus meaning "a green shoot" or "twig," is the undifferentiated vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens.
A prothallium or prothallus is usually the gametophyte stage in the life of a fern or other pteridophyte.
A hypha is a long, branching filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth and are collectively called as a mycelium. Yeasts are unicellular fungi that do not grow as hyphae.