Questions & Answers about Poslední pes čeká u dveří.
Because pes is the subject of the sentence, so it is in the nominative case.
- pes = nominative singular, dog
- psa = usually accusative singular or genitive singular
In Poslední pes čeká u dveří, the dog is the one doing the action of waiting, so nominative is required.
Poslední is an adjective meaning last or final, and it has to agree with pes in:
- gender: masculine animate
- number: singular
- case: nominative
So poslední pes means the last dog.
A useful thing to know: poslední belongs to a type of adjective whose ending is often -í, so this form is normal.