I answered "yellow plates" but was told this was supposed to be "yellow boards"? Is this correct?
I recommend three resources for word definitions while making one's way through the Duolingo exercises.
Google Translate and
for deep dives into word history, Historische woordenboeken from het Instituut van de Nederlandse Taal.
I use all of these quite frequently. Don't rely solely on Google Translate, but it is useful as part of elementary research. You can even paste a copy of the URL from a dictionary entry into the "from" field, and a link to a translated page is generated. Again, be careful relying to heavily on the Google translations, because it loses some of the subtleties of the language. But it's a decent assistant.
For Dutch grammar tips written in English, in addition to the ones within Duolingo, I like dutchgrammar.com.
Now. As for "borden," using the above sites, we learn (or already knew) that it's the plural of "bord". According to Van Dale, we find this for "bord":
1 houten blad bij verschillende spelen: dambord, schaakbord
2 groot plat oppervlak voor opschriften: uithangbord; een bord voor zijn kop hebben niet gevoelig zijn voor bedekt geuite kritiek, stille wenken enz.
4 ronde plaat of schaal, m.n. om van te eten
Plugging that text into Google Translate, we get
1 wooden blade at different games: checkerboard, chessboard
2 large flat surface for inscriptions: signboard; a plate in front of his head have not been sensitive to covered criticism, silent hints etc.
4 round plate or bowl, ie to eat
Obviously, the translation isn't perfect, but we can gather that "bord" can mean both a plate from which one eats and a board (used for a sign or a game, etc.).
Oh. I also often use the English Wiktionary, because it has pretty good etymologies, and under "board" we find
From Middle English bord, from Old English bord (“board; plank; table; shield; deck; ship; boundary”), from Proto-Germanic burdą (“board; plank; table”), from Proto-Indo-European bʰerdʰ- (“to cut”).
So Dutch "bord" and English "board" are, in fact, the same word. It is no accident that the English phrase "room and board" describes a lodging place where you get a room to sleep and food to eat--the "board" part represents food. And that is food that you would eat from a plate.
By the way, I crept further into "a plate in front of his head have," and the better translation would be "to have a plate in front of his head." What immediately follows that phrase is the definition: To not be sensitive to veiled criticism or silent hints, etc. So I gather that saying someone has a board in front of his head is an idiomatic expression that means he's not taking the hint, like someone impervious to social cues about when it's time to leave a party, for example. (That's me sometimes, like when I get excited about looking up words and telling people about them.)