The category which includes related families is:

 # The category which includes related families is:

 A. Phylum

 B. Order

 C. Class 

 D. Genus

The correct answer is B. Order.

Phylum: A phylum is a higher taxonomic category that includes related classes. It represents a major division of organisms based on certain fundamental characteristics. 

For example: The phylum Chordata includes all animals with a notochord (such as vertebrates). Within the phylum Chordata, we have classes like Mammalia (mammals), Ayes (birds), and Reptilia (reptiles).

Order: An order is a group of related families that exhibit a few similar characters. In the plant kingdom, families like Convolvulaceae and Solanaceae are included in the same order (e.g., the order Solanales). Similarly, in the animal kingdom, families like Felidae (cats) and Canidae (dogs) are included in the same order Carnivora.

Class: The class is a higher taxonomic category that includes related orders. It represents a broader grouping of organisms. For example: In the plant kingdom, orders like Solanales and Rosales are included in the same class Magnoliopsida (dicotyledons). 

 

In the animal kingdom, orders like Carnivora (cats, dogs) and Primates (humans, apes) are included in the same class Mammalia. 

Genus: The genus is a more specific taxonomic category that includes related species. It represents a group of species that share a common ancestry and broad features of organization. For example, the genus Panthera includes species like lions (Panthera leo) and tigers (Panthera tigris).