What’s the difference between 符合, 适合 and 适应?
符合 means "match". Example:


  他 符合 我们的 要求。
  
  He matches our requirement.


适合 means “fit” in a sense of "good fit". Example:


  他 很 适合 这个 职位。
  
  He is a good fit.


符合 and 适合 have similar meanings but are often paired with different nones. I would say 符合 is a more precise fit than 适合。

适应 mean something quite different. It means "get used to", it is the process of getting to 符合 and 适合.