Couldn't the correct answer also be "that egg, those eggs" or "this egg, these eggs"?
No that would then be diese oder dieses oder dieser I believe. "der", "die" and "das" all literally translate to "the".
This type of sentence is really helpful for remembering genders, articles and plurals, I'd love to see more examples of this please!
Very very nice thing! I will suggest it in the Feedback field straight away!
All of them? no exceptions? this would be very helpful for my memorization/learning of der/die/das.
Yes. All nouns use "die" in their plural form, regardless of the gender of the singular form.
der Mann, die Männer
das Ei, die Eier
die Katze, die Katzen
Edit: I forgot to mention that when you learn about dative and genitive cases, the rules are a little different.