Questions & Answers about Kad je zrak hladan, držim usta zatvorena.
Both kad and kada mean when.
- kad is shorter and very common in everyday speech
- kada is slightly more formal or a bit more emphatic
So both of these are fine:
- Kad je zrak hladan, držim usta zatvorena.
- Kada je zrak hladan, držim usta zatvorena.
In normal conversation, kad is extremely natural.
Because je is a clitic form of biti (to be), and Croatian clitics usually go in the second position in their clause.
So the natural order is:
- Kad je zrak hladan
not:
- Kad zrak je hladan
This is a very common Croatian pattern. English speakers often expect the verb to stay after the subject, but Croatian clitics follow different placement rules.