What is difficult to determine in the process of adaptation unless there is a closely related species to which you can compare findings?

This question was slightly confusing, but I came up with this answer, and as per my understanding, I'd go for this response:

Species that are widely different may have very different metabolic processes and external processes, and their behavior may change towards a certain ecological event or feature. For example, one organism may combat the winter weather by migrating to a warmer location, while another organism of a different species may deal with winter weather by hibernating. In this scenario, you cannot compare and contrast the info that much as their processes, behavior, and genetic basis is completely different. You can best compare adaptations of two like species, as they may have similar structures and behaviors.

Hope this helps!

the correct option is option d