Questions & Answers about Stijenka je tanka.
- stijenka = a noun, the subject of the sentence
- je = is, the 3rd person singular present tense of biti (to be)
- tanka = an adjective, describing the subject
So the structure is:
noun + is + adjective
This is a very common Croatian sentence pattern.
Because tanka has to agree with stijenka.
In Croatian, adjectives change form to match the noun in:
Here, stijenka is:
- feminine
- singular
- nominative
So the adjective must also be feminine singular nominative:
- masculine: tanak
- feminine: tanka
- neuter: tanko
That is why tanka is the correct form here.