Which one of the following is a single cell fungi

Yeast is a single cell fungus.
Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom.
Yeasts are unicellular organisms with some species having the ability to develop multicellular characteristics by forming strings of connected budding cells known as pseudo hyphae or false hyphae.
Yeast sizes vary greatly, depending on species and environment, typically measuring 3 - 4 µm in diameter, although some yeasts can grow to 40 µm in size.