Na pismenom ne smiješ prepisivati, a na usmenom ne možeš prepisati odgovor s papira.

They are short for na pismenom ispitu and na usmenom ispitu — literally on the written exam and on the oral exam.

In Croatian, the noun ispit is often left out when it is obvious from context, and the adjective stays behind as if it were a noun. This is very common.

So:

• pismeni ispit = written exam
• usmeni ispit = oral exam
• na pismenom = on/in the written exam
• na usmenom = on/in the oral exam

Because they are in the locative singular, after the preposition na.

Here the hidden noun is ispit, which is masculine singular, so the adjective agrees with it:

• pismeni ispit
• na pismenom ispitu

When ispitu is omitted, the adjective still keeps the same form:

• na pismenom
• na usmenom

So the -om ending shows the case and agreement.

In Croatian, na is commonly used for events, activities, and occasions such as:

• na sastanku = at the meeting
• na predavanju = at the lecture
• na ispitu = at/on the exam

So na pismenom and na usmenom are the natural Croatian way to say in/on the written/oral exam.

English and Croatian do not always use the same preposition here, so it is best to learn this as a set phrase: na ispitu.

This is an important difference:

• ne smiješ = you must not / you are not allowed to
• ne možeš = you cannot / you are not able to

So in the first clause, the sentence talks about a rule or prohibition:

• Na pismenom ne smiješ prepisivati
  = On the written exam, you are not allowed to copy/cheat.

In the second clause, it talks about practical impossibility:

• a na usmenom ne možeš prepisati odgovor s papira
  = and on the oral exam, you cannot copy the answer from paper.

So the contrast is:

• written exam: it is forbidden
• oral exam: it is not really possible

This is a question of aspect, which is very important in Croatian verbs.

• prepisivati = imperfective
• prepisati = perfective

Here is the basic difference:

• imperfective focuses on the activity in general, repeated action, or ongoing action
• perfective focuses on a completed act or result

So:

• ne smiješ prepisivati = you must not engage in copying/cheating
  This sounds like a general rule.
• ne možeš prepisati odgovor = you cannot copy down an answer
  This refers to a single completed act: getting the answer from the paper.

That is why the aspect changes.

In school and exam contexts, prepisivati / prepisati often means to copy from someone/something dishonestly, so in English it can mean:

• to copy
• to cheat
• to copy off someone
• to copy from notes/paper

Outside school contexts, it can also mean more neutrally to copy out or to transcribe.

In this sentence, because it is about exams, the dishonest meaning is the natural one.

Because odgovor is the direct object of prepisati, so it is in the accusative singular.

For a masculine inanimate noun like odgovor, the accusative singular looks the same as the nominative singular:

• nominative: odgovor
• accusative: odgovor

So the form does not change.

If the noun were masculine animate, you would often see a different form.

Yes, s/sa can mean with, but it can also mean from/off depending on context.

Here it means from or off:

• prepisati odgovor s papira = to copy an answer from a piece of paper

The noun papir becomes papira because s/sa takes the genitive in this meaning.

So:

• papir = paper
• s papira = from the paper / off the paper

This is completely normal Croatian usage.

Both s and sa are forms of the same preposition.

Croatian usually uses:

• s before most words
• sa when pronunciation is easier that way, especially before certain consonant clusters

Since papira begins with a simple p, s papira is the normal form.

So this is mostly a matter of sound and pronunciation, not meaning.

Because Croatian often leaves out subject pronouns when they are already clear from the verb ending.

Here:

• smiješ = you are allowed
• možeš = you can

The ending -š already shows 2nd person singular, so ti is unnecessary.

Croatian uses subject pronouns mainly for:

• emphasis
• contrast
• clarification

So ne smiješ naturally means you must not without needing ti.

Here a is a coordinating conjunction that often expresses a contrast or comparison between two situations.

It can often be translated as:

• and
• while
• but

In this sentence, a introduces a contrast:

• on the written exam, you are not allowed to copy
• on the oral exam, you cannot copy from paper

So a is something like and on the other hand or while.

It is not exactly the same as i, which is a simpler and.

Yes, absolutely.

The full version is:

• Na pismenom ispitu ne smiješ prepisivati, a na usmenom ispitu ne možeš prepisati odgovor s papira.

That is more explicit.

The shorter version without ispitu is very common and natural when the context already makes it clear that we are talking about exams.

No, Croatian word order is fairly flexible, though some versions sound more natural than others.

The given sentence is natural because it puts the exam type first:

• Na pismenom ne smiješ prepisivati, a na usmenom ne možeš prepisati odgovor s papira.

This highlights the contrast between written and oral exam.

You could also say:

• Ne smiješ prepisivati na pismenom, a na usmenom ne možeš prepisati odgovor s papira.

That is still understandable, but the original version sounds better if the main point is the contrast between the two exam types.

No. They are adjectives meaning:

• pismeni = written
• usmeni = oral, spoken

For example:

• pismeni odgovor = written answer
• usmeni odgovor = oral answer
• pismeni ispit = written exam
• usmeni ispit = oral exam

In this sentence, they clearly refer to exam types because the context makes that obvious.