Answer:
Animalia
Step-by-step explanation:
There are several kingdoms that have eukaryotes (multicellular organisms) three of these kingdoms are mainly composed of these organisms(multicellular). The forth has only some multicellular organisms. So a multicellular organism is most likely to be a part of the main 3 eukaryote kingdoms:
Plantae (plants)
Fungi (fungus)
Animalia (Animals)
The animal kingdom is the largest with over 1 million species, therefore statistically it is most likely for a multicellular organism to be part of this kingdom.