Why does Duolingo say that 中 is pronounced "naka" but spelled ちゅう?


I am currently doing the beta course for Japaneses on duolingo. In one of the
lessons, I was confronted with this question which I kept getting wrong:

[![enter image description
here](https://i.stack.imgur.com/WHqcI.png)](https://i.stack.imgur.com/WHqcI.png)

When I play the sound, the voice clearly says "naka", which I think is なか, but
the answer is ちゅう, which I beleive is pronounced "chuu".

What is happening here?




When standing alone, you would be right in saying that the character 中 makes
the sound なか, but you need to remember that kanji can have multiple readings
(訓読み and 音読み for Japanese readings and Chinese readings). When used in certain
words, like 中学校 (read ちゅうがっこう, meaning middle school), the pronunciation can
change, in this case being ちゅう. The other two options there, わたし and ごく are
never going to be readings for 中.

Also, ちゅう sounds more like "chuu"

