Final answer:
A monophyletic group, also called a clade, includes a common ancestor and all of its descendants, representing a branch on a phylogenetic tree that reflects evolutionary relationships.
Step-by-step explanation:
A monophyletic group, also known as a clade, is a grouping in a phylogenetic system that includes all of the descendants of a common ancestor. The correct answer to the question is therefore (c) Group consisting of a common ancestor and all its descendants. A phylogenetic tree is a diagram reflecting the evolutionary relationships among organisms, and the branches represent these relationships. A clade is a specific branch of the phylogenetic tree that starts with a single ancestor and includes all of its descendants, no matter whether they are extinct or living. It is important to recognize that clades can be of varying sizes and they help elucidate the evolutionary history of organisms, showcasing which traits have been derived and shared across different lineages.