Ans. (C). class.
Cats and humans, both are eukaryotic organisms that belong to phylum chrodata and sub-phylum vertebrata. According to studies, humans and cats have 90% DNA similarities. The most specific level of classification, shared by humans and cats is 'class' as both belongs to same class.
Both humans and cats belong to class mammalia, which include organisms that produce live young, have mammary glands for feeding of young, and possession of fur or hair on body.
Thus, the correct answer is option (C).