A microorganism has the following characteristics: Its cells have a nucleus and cell walls, it is multicellular, and it grows in long filaments. What is its general classification?

It must belong to the Kingdom Fungi.

Explanation:

Fungi are the organisms that have long thread-like structures called hypha in their body. Many hyphae together form a mass called mycelium. Fungi are eukaryotes and have a well-defined nucleus in their cells. They also have cell walls that are made up of chitin. Fungi are mostly multicellular. However, yeast is the fungi that have a single cell in their body. Fungi are heterotrophs and derive their nutrition by parasitic or saprophytic mode of nutrition. Therefore, the given description tells that the microbe should be a fungus.