Correct answer: B). Sac Fungi
Yeast is the single-celled microorganism that is classified with the molds and mushrooms in the kingdom Fungi. It is a member of Group Ascomycota, which is also known as sac fungi.
A truffle is the fruiting body of the subterranean ascomycete fungus. These are found in close association with the tree roots as it is an ectomycorrhizal fungus.
Hence, the correct answer would be option B.