"A strawberry is a fruit."
Translation:Frago estas frukto.
The verb to be (esti) works as a copular or linking verb, that links two parts in the same case and does not take an accusative.
The accusative case is not used with the verb esti. jxetkubo already said this, but he didn't reply to you, so you might not have been notified.
Why isn't it, "Frago estas frukton"? The whole add an "n" part is very confusing. Sometimes the n is added, sometimes it's not. Sometimes it's added on some of the object words in a sentence, while other objects in the same sentence don't have it. Duolingo expects us to just pick up on these unexplained rules. But there should be some type of explanation in a note or something before the lesson. Can someone explain why some sentences use the n and some do not? Thanks in advance. (Sorry if I sound whiney. It's just a bit frustrating. I want to learn the correct rules, so I can practice right, instead of just guessing each time.)