"Kateřina is not thinking about the last horse."
Translation:Kateřina na posledního koně nemyslí.
"Kateřina o posledním koni nepřemýšlí." is correct too. But is better for this sentence "Kateřina na posledního koně nemyslí.
Think = myslit (na - of), přemýšlet (o - about, over), ...
Remember = pamatovat (si), rozpomenout se na, zmínit se o, připomenout. (Dát spropitné číšníkovi /the waiter/)
Memorize = memorovat (nebo-li - učit se zpaměti)
Because it's wrong.
To can be translated as It, that, but in Nominative case.
Kateřina nemyslí na to posledního koně
Kateřina is not thinking about it last horse.
It shoud be in accusative case.
Kateřina na toho posledního koně nemyslí.
Kateřina nemyslí na toho posledního koně
I'm native AmE. I would suggest that "A last horse" is more conceptual than concrete, and probably wouldn't be used to much in conversation.
"THE last horse" refers to a specific horse: the horse that was "last" in some particular situation.
And "THAT" last horse would usually have the same general meaning, but would be more specific or emphatic. It might also have some directional context -- for example, there are two groups of horses, and one was "last" in each group, but you're referring or pointing to a certain one of the two "last horses."
a last horse - I am not sure if it is even possible, but some general concept of a horse that is last
the last horse - simply the horse that is last, the last one
that last horse - more strongly ponting at the last horse, reminding that we have already spoken about it "that last horse we were discussing yesterday" or pointing "look at that last horse overthere"
Native English speakers may want to clarify this.
Edit: The explanation of that last horse by BoneheadBass also conforms to where I would use the Czech "ten poslední kůň".