Answer :

An order is subdivided into several families.

is 100% the right answer

Answer: The correct answer for the fill in the blank is  families.

There are eight hierarchical categories used to classify organisms. Order is one of the hierarchical categories used in classifying organisms. It is subdivided into several families. It means that families occupy lower place  in the taxonomic categories.

Example- Grasses belong to the order Poales and it belongs to one of its families, which is called Poaceae.