You can treat it as different words that have the same form ;)
"to" can mean "is" in 'X is Y' sentences when both X and Y are noun phrases.
"to" is a neuter pronoun meaning "this": "to dziecko" = "this child"
"to" may be the subject of the sentence, thus meaning this/that/these/those in "This is Y" sentences. It does not change neither because of gender nor number in such situations.
I wanted to tell you that this sentence is OK in Polish, but it turns it's OK in English, too,
Felidae is the family of cats. A member of this family is also called a felid.Living cats belong to the subfamilies: Pantherinae – comprising the tiger, lion, jaguar, leopard, snow leopard and clouded leopards Felinae – including all the non-pantherine cats
Also Polish word for Felidae is "kotowate"
At the top of this discussion (in the mobile app) the English translation is displayed as "A lion is an animal", even though the preferred translation appears to be " A lion is a cat" when actually answering the exercise.
I believe that might be what the wtfers are attempting to articulate.
No. With "X is Y" construction, when Y is a noun phrase, you either use:
X + "to" + Y in Nominative
X + a form of "być" + Y in Instrumental.
So it's either "Lew to kot" or "Lew jest kotem".
There are of course more nuances, you can read about them here: https://www.duolingo.com/comment/16373167