The correct answer is A. That they shared a common ancestor
Step-by-step explanation:
In evolution, similar structures such as bones, organs, etc. in different species are often classified as homologous structures, this implies different species or organisms share a common ancestor and therefore there are similarities between them, but also differences as each species needed to adapt to different environmental conditions and evolved in different ways over time. This leads to structures that are similar but not identical and might differ in function, which occurs in the case of the leg bones of orangutan, dog, pig, etc. that are all mammals deriving from the same ancestor and thus share similar leg bones but with specific features or differences. Thus, the diagram suggests that mammals share a common ancestor.