Final answer:
When someone says, "Wow! I can tell you all are family -- you all resemble each other so much!" they mean that there are several features that all members of the family have in common.
Step-by-step explanation:
When someone says, "Wow! I can tell you all are family -- you all resemble each other so much!" they mean that there are several features that all members of the family have in common (option a). Members of the same species, including humans, share both external and internal characteristics, which develop from their DNA. The closer the relationship between two organisms, the more DNA they have in common and the more characteristics they share (from the given sources).