The phylogenetic tree is based around three branches, eukrya, archaea, and bacteria. In order to place an organism in the broadest taxonomic classification, it will go under eukarya in this case, as it is the only one from the three basic ones from the choices provided. Eukarya is the branch where we have multi-cellular organisms, and it is the one that has given rise to the best known organisms on the planet, the largest ones, most attractive etc. The animals and plants fall into the category of eukarya and are its most marking members, thus the humans are part of it as well.
