As a non-native English speaker who has struggled with all different idioms, prepositions, expressions and accents, etc. I can understand why this is happening.
English is being taught like mathematics, especially at the elementary level. For example, when you are asked "How are you?", the only reply you would learn is "Fine, thank you and you?" as if there were no other alternatives. That's the elementary level English. The linked question seems to have the same pattern. The only logical and idiomatic reply seems to be D (Nothing). But some would argue B (no matter) is better because it is short for "It is no matter".
No matter what the right answer is, I don't believe everything a questioner says when it comes to who says what is right. I have witnessed a few occasions on English Language Learners (ELL) where a questioner said their teacher couldn't even tell the right answer from the wrong one when there was nothing confusing at all.
They could be lying, or they could have misunderstood something. But they learn something through this process and as @DanBron mentioned, there seems to be nothing ELU can do about it except that we ask those OPs to go to ELL, which I just did.