I wish that on these exercises that they would translate the sentence to English as I can't remember what droog means.... :s
By the way, I decided to try coming up with something to help me remember the meaning of "droog", and I want to share it in case it helps others, too. "Droog" backwards is "goord", which is quite similar to "gourd", something that would often be used to carry water. But since you have to flip the word around to get that meaning, "droog" must be the opposite: it describes something that doesn't carry any water!
I also have a pretty hard time remembering that one! However, here's some general information that might help you in tough situations: If you're using a web browser, you can move your mouse over any word to view some possible translations. If you're using the mobile application, you can tap on any word to do the same. (Try it now at the top of this discussion page!) The ability to do this is always indicated by the small dots underneath the words.
Note that not all of the translations that pop up are necessarily valid translations in the context of the sentence you're practicing, though! For example, you might see "she" and "they" as possible translations for "ze"; but if the sentence reads, "Ze heeft honger", only one of those translations could be correct!
also be aware that if you do this duolingo will register that you aren't confident about that word (so if you do know it it is better not to check)
If in Dutch, adjectives attached to a plural noun always take the extra '-e', how come paarden doesn't?
That is only true when the adjective comes before the noun. In this sentence "droog" is a predicate adjective (connected to its noun by a linking verb "zijn"), which never the get -e ending.