A.Hypha – a filament of mycelium is called hypha.
B.mycelium – a network of filamentous structure that forms the body of fungus is called mycelium.
C.Rhizoid - root like hyphae appear in some fungi are called rhizoids.
D.Fruiting body – specialised structure formed after fertilizaiton in ascomyetis and basidiomycetis fungi is called fruiting body. It is made up of secondary mycelium.
So, the correct option is ‘mycelium’.