męż + czy + zna: the first one comes from old Polish mąż, now only meaning "husband"; the second is the conjunction czy = 'whether' or 'if' or the particle that starts a question; the third one means "knows".
mężczyzna = husband + whether + knows = whether the husband knows :-) This is the question!
Man eats should to be correct! Why? I am supposed to translate it into English and in English, I can too say Man eats and be correct. "A" is implied. Man eats. Men eat. All I need for a grammatically correct sentence is a subject (Noun) and a verb. Man eats is therefore, correct.
However, if you want us to translate it into Professor's long winded English, then say so. And tell us that ALL sentences MUST use "A" whenever it can logically be used!
But, do keep in mind folks - Duolingo ALWAYS requires "A" where you wouldn't need it to be grammatically correct in short sentences where "A" would otherwise be implied. And, WE fools make the same argument over and over again and Duolingo does NOT agree! I forget this! When I learn French, I will revisit this same stupid argument again! When I learn Russian, I will again kvetch like a raving fool that I am! Oy vey! Maybe someday I will learn that Duolingo wants the longest sentence that is still conceivably correct in their translations. I prefer LearnWithOliver for a reason. I do not need to guess as to how that English sentence MUST read in order to be correct when other versions are still technically correct.
And, this is why I am NOT reporting this as a mistake because I am not convinced that Duolingo will ever see it as a mistake. This conversation has been had in Irish and in German if my memory serves me right.
EDIT - Just changed "every" to "ever". My own mistake was glaring at me. ;)
It looks as though there is another word for "mankind": "ludzkość" Yet "człowieczeństwo" and "mężczyźni" can also be used to mean "mankind". https://translate.google.com/?hl=en#auto/pl/mankind We could use a Polish expert to step in and let us know more.
I think it also depends on whether you're thinking way back to First Year in school. I did try to do a google search, and came up with google not understanding what I wanted. I wouldn't think that "man" needs to have "a" in order to not refer to mankind. In the Bible, "man" often refers to both men and women. However, my beef may be colloquial slang in nature, and I'm just not aware of that. So, I'll drop it now. I can't find my early readers anyway.