Questions & Answers about Flaša ulja je u kolicima.
Because ulja is the genitive singular form of ulje.
In Serbian, after a container noun like flaša (bottle), you normally use the genitive to express a bottle of ...:
- ulje = oil
- ulja = of oil
So:
- flaša ulja = a bottle of oil
This is very common in Serbian, just like:
- čaša vode = a glass of water
- šolja čaja = a cup of tea
Flaša is in the nominative singular because it is the subject of the sentence.
The sentence is built like this:
- Flaša ulja = the bottle of oil
- je = is
- u kolicima = in the cart / stroller / trolley
Since flaša is the thing being talked about, it stays in the nominative.
Also, flaša is a feminine singular noun.