Where and when does fertilization occur in the mushroom life cycle?

• A. Underground, as a mycelium begins to spread
• B. On the surface of the ground, when a basidiospore germinates
• C. Underground, when the hyphae of different mating types fuse
• D. In a mushroom, when eggs and sperm meet
• E. In a mushroom, when the nuclei of a dikaryotic cell fuse