Why Do the Authors of Your Textbook Reject Definitions of Family

Why do the authors of your textbook reject definitions of family that depend on particular types of people (like parents) and specific types of ties (like marriage) ?

A) They believe that the nuclear family remains the most important prototype for a family.
B) They want the definition to be broad enough to encompass a variety of living arrangements.
C) They believe that, in the future, more and more families will consist of two sets of parents with children.
D) They argue that it is important to limit the definition of families so that families can be discussed with clarity.