"Is this fresh food?"
Translation:Це свіжа їжа?
It's quite easy: "це" is a declinable word "цей" when it modifies a noun, at least an implied one, and here it does not (this is a subject; fresh food is a copula complement).
You may imagine it as the difference between my/mine, your/yours. In English, you only use "my" as a modifier. Instead of "My is better" you should use "Mine is better".