Ans. (a). kingdom.
According to seven system of classification, the most common level of classification is kingdom as Jellyfish, earthworms, and humans are all belong to common kingdom, animalia.
They multicellular, eukaryotic, heterotrohic organisms that cannot make their own food. Jellyfish, earthworms, and grasshoppers are classified in the sub-phylum invertebrata, while humans are classified in the sub-phylum vertebrata.
Thus, the correct answer is option (a).
