The correct option is A Mushroom
Pelomyxa is a protist and 500-800 μm in size.
Chaos is a protist and 5 mm in length.
Saccharomyces is a fungus and has a diameter of 2 - 8μm and length of 3 - 25μm. Hence cannot be seen without a microscope.
Mushroom is a fungus and can be seen with naked eyes. Hence, option A is correct.