They share a common ancestor.
They compete for resources.
One organism evolved into the other organism.
Answer: The correct answer is -
They share a common ancestor.
Explanation:
Evidences for the common descent of living organisms (that is whether they have evolved from the same ancestor) have been elucidated through phylogenetic tree.
A clade (also called monophyletic group) is considered as a group of individual organisms, with common ancestor and its descendants. It indicates a single "branch" on the phylogenetic tree (also known as "tree of life).
Therefore, two organisms belonging to the same clade share common ancestor.