It is. When I see a d now I don't even try to pronunce it, I say l, or just d, depends of the place in the word. And it is not what the others don't understand. Here, i say "val spiser du ?" but I write "Hvad spiser du ?" If people think I am some sort of foreigner trying to speak danish, well, they are right.
You shouldn't have been marked wrong for that - unless you were answering an audio question. In which case, you're supposed to type what you hear, not translate what you hear (I've done this on a few occasions myself). If it was a written question though, you should report it.