"Are you a director?"
I answered "yonetmen misin" and it was correct. How can "Müdür müsünüz?" be "are you A director?" if it is plural?
"siz" is formal singular as well. You are not sure if you are talking to one or multiple people :)
Why is Müdür müsün? wrong?
OK, I have to edit: when I had this in multiple choice I chose both Müdür müsün? and Müdür müsünüz and was marked wrong because only the plural was right. Then later I got it as an open question so I tried the singular again and it was marked right. Apparently there is a mistake in the rating of the multiple choice version.
Director can be translated as müdür and yönetici same meaning but the yönetmen is totally different and secondary meaning a kind of a movie director is yönetmen in Turkish language anyways.
It is ok and I added it. Keep in mind though that it may sound a little weird in some contexts. "bir" isn't normally used with occupations even though it isn't technically grammatically incorrect.