Final answer:
Hyphae join up to form a mycelium, which can lead to the development of a basidiocarp, the fruiting body of a mushroom-producing fungus. The correct option is B.
Step-by-step explanation:
When hyphae join up, they form a structure known as mycelium. This mycelium forms the dense and interconnected network that makes up the main body of a fungus. The mycelium is crucial for the absorption of nutrients and is the basis for the growth of fungal reproductive structures, like mushrooms.
In Basidiomycota fungi, when conditions are right, this mycelium can ultimately produce a basidiocarp, which is the fruiting body more commonly recognized as a mushroom. The basidiocarp supports the development of basidia on its gills or surface, which are responsible for producing basidiospores after a process that includes karyogamy and meiosis.