What makes any of those words "de" or "het"? It's not in the sentence itself so how am I supposed to know? I know plural and gender obvious words (like man or girl) are de, but I'm unclear on the rest of the rules.
It's just grammatical gender, only instead of masculine and feminine, it's masculine/feminine and neuter. Like is always the case with grammatical gender, which word is going to be het vs de is pretty much random, with a bit of a pattern emerging only in words having to do with people.