Da li ste juče otvorili prozor i vrata?

Da li is a very common way to introduce a yes/no question in Serbian.

So here it signals that the sentence is asking something like Did you... ?

It does not have a separate lexical meaning like if or whether in this sentence; it mainly marks the sentence as a question.

A very common alternative is: Jeste li juče otvorili prozor i vrata?

That means the same thing.

Ste is the 2nd person plural form of the auxiliary verb biti (to be) in the present tense.

In Serbian, the past tense is usually made with:

• an auxiliary form of biti
• plus a past participle

So:

• ste = auxiliary
• otvorili = past participle

Together, ste otvorili means you opened / you have opened.

Also, ste can refer to:

• you all
• or you in a formal/polite singular sense

Otvorili is the past participle of otvoriti (to open).

It is used here with ste to form the past tense.

The form otvorili is the usual plural form used with vi / ste. So it fits a sentence addressed to:

• more than one person
• or one person formally

If the speaker were clearly talking to a group of women, you could hear otvorile instead.

This is about aspect, which is very important in Serbian.

• otvoriti = perfective
• otvarati = imperfective

In this sentence, otvorili is perfective, so it asks about a completed action: whether the window and the door were opened.

If you used otvarali, it would sound more like:

• were you opening
• did you open repeatedly
• were you in the habit of opening

So otvorili is the natural choice when asking about a single completed event yesterday.

Juče means yesterday.

Its position is natural here:
Da li ste juče otvorili prozor i vrata?

One important reason is that ste is a clitic, and Serbian clitics usually have to stand very near the beginning of the clause. So:

• Da li ste juče otvorili... = natural
• Da li juče ste otvorili... = not natural

You can move juče in some contexts, but this version is very standard and smooth.

They are both in the accusative case, because they are the direct objects of otvorili.

You opened what?

• prozor
• vrata

Why do they look the way they do?

• prozor is a masculine inanimate noun, and for masculine inanimate nouns, accusative = nominative
• vrata has the same form here as its nominative/accusative plural

So even though English would show object function by word order alone, Serbian shows it through case, even when the form happens to look unchanged.

Because vrata is one of those Serbian nouns that are grammatically plural even when they can refer to a single object.

This is similar to English words like scissors or pants, which are plural in form.

So:

• vrata = door / doors, depending on context
• grammatically, it behaves like a plural noun

That is why you learn it as vrata, not as a regular singular noun like prozor.

Serbian normally does not use articles like English the and a.

So:

• prozor can mean a window or the window
• vrata can mean a door / the door / doors / the doors, depending on context

The listener understands which one is meant from the situation, previous conversation, emphasis, or added words.

That is very normal in Serbian.

Yes.

Ste and otvorili can be used when speaking to:

• more than one person
• one person formally/politely

So this sentence could be addressed to:

• a group of people
• or one person whom the speaker addresses as Vi

You usually know which meaning is intended from the context.

Yes. A very common alternative is:

Jeste li juče otvorili prozor i vrata?

This is basically equivalent to:

Da li ste juče otvorili prozor i vrata?

In everyday speech, people may also rely on intonation, but for learners, the two safest standard patterns are:

• Da li ste ... ?
• Jeste li ... ?

Both are very useful and very common.