The body of a mushroom is made up of slender filaments called hyphae. xylem. phloem. rhizoids.

The correct answer is- Hyphae.

Mushroom belongs to the kingdom fungi, which includes any group of eukaryotic organisms that are having microorganisms such as yeast, moulds, and mushrooms.  

Many species of fungus exhibit slender, filamentous structures, known as hyphae. In most fungi, hyphae are considered as the primary mode of vegetative reproduction and  form a vegetative part of fungus, termed as mycelium.

Therefore, the slender filaments that make up the body of a mushroom are called hyphae.