How Does the Phenomenon of Horizontal Gene Transfer Muddle the Concept

How does the phenomenon of horizontal gene transfer muddle the concept of monophyletic groups?

A) Horizontal gene transfer makes it impossible to distinguish monophyletic groups.
B) Monophyletic groups are based on the concept that a particular group of species descended from a common ancestor. When horizontal gene transfer occurs, not all of the genes in a species were inherited from the common ancestor.
C) Since horizontal gene transfer includes transfer from one group of species to another group with a common ancestor, there is no muddling of the concept of monophyletics.
D) All of these are correct.