I have a question about the Hangul Master Quiz.

Hello! I am studying with a book called 'Mastering Hangul,' and I have a question about a part of the quiz that I don't understand. In quiz 32 of unit 8, I tried to listen to the audio file and guess the answer, but it sounded like '넘는' to me. However, the options in the book were 1. 널믄 2. 넓은 3. 넙른. The correct answer is stated to be number 3, but I don't understand why. Does anyone know why the answer to this question is number 3? You can listen to the audio file [here](https://audio.talktomeinkorean.com/?id=23). I would really appreciate any help!