"They are old animals."
Translation:Jsou to stará zvířata.
Hi, if you did not use "to", the sentence would have a different meaning.
Jsou stará zvířata. -> means old animals exist (there are animals in the world that are old)
Jsou to stará zvířata. -> is talking specifically about certain animals and saying that those are old.
The phrase "je to/jsou to" is commonly used in Czech to identify people/things/etc. (There are many sentences that you've already seen here in this course before. - Je to muž., Jsou to ženy., Je to město., Jsou to psi., etc.) Notice that "to" does not change with gender of a noun when using this phrase, only the verb has to match in singular/plural.
I'm not entirely sure if you're asking about the interchangeable "ona/to" in the above sentence, but if so; they are interchangeable and "to" is what majority of people would use. The sentence flows better with it, but in understanding the sentence, there is no difference.
I am finding it a very slow process to recognise Czech words ! Edit: and at Crown 3 still not on top of this little section. Maybe the 5 Crowns will do it. Note: I've switched from tablet to 2 screens laptop for Czech as having the grammar notes always open on another screen helps. (I haven't seen anyone else mention this all over Duo!)
Thank you for your tip. I have seen 'infola' mentioned somewhere. But you did not give me the title. I am not in the Czech Republic. I'll be in Paris tomorrow. But I suppose mail order is the way. You'll see I am very (!) experienced with Duo, and occasional exchanges about learning efficiency, or not, can be appropriate in these multiple forums. By the way, I have very much improved my use of the Czech tips pages since that expression of frustration. I don't see infola here : http://www.czech-in-prague.cz/index/czech_textbooks/0-14 http://ujop.cuni.cz/en/outline-of-essential-czech-grammar-for-foreign-students http://www.locallingo.com/czech_language_books.html
Probably referring to "infoa", perhaps this book: https://www.infoa.cz/zbozi/the-course-of-czech-grammar-vyprodej/?poskozene Even with that book, though, IMHO in the case of Czech, DuoLingo is better used as a supplement, rather than the primary learning method.