Actually, the rule says that "ντ" is supposed to sound as "d" if it's at the beginning of the word, and "nd" if it's inside the word. However, many tend to pronounce it as "d" in all cases, but it's wrong. Furthermore, it never sounds like "nt" - unless it's foreign word or name transcribed in the Greek alphabet.
Actually the word in greek is not "άντρας". It's "άνδρας". The correct pronunciation is really difficult for someone who can't say "δ" perfectly. So if you say "andras" and pronounce the "δ" as "d", it sounds wrong. It's better to say "adras", which is the correct pronunciation of "αντρας" and we also use it in the greek everyday-language.
I wrote άνδρας, instead of άντρας, which is actually concidered as correct here in greece. thats the original way of writting the word man, which has origins from ancient greek, ὁ ἀνήρ , του ανδρός . Still though, it was taken as a mistake and there is no report option for '' my answer should be correct'', or however it should be.
Listening exercises can only accept one form, as far as I know.
And you are expected to type what you hear -- since the voice says [andras] and not [anðras], you have to type άντρας and not άνδρας.
In a translation exercise (English to Greek) for this sentence, both forms should be accepted.