I was making my Duolingo course, and I found the following sentences:
Es sind starke Studenten.
Das sind die starken Katzen.
Something here seems off. "The students" is clearly a plural, but it uses the pronoun "es". I would have thought the right pronoun here would be sie. Same with cats. I would have used "die":
Sie sind starke Studenten.
Die sind die starken Katzen.
What is going on here?