Moja siostra woli cukinię z ryżem, a ja wolę kapustę z makaronem.

Because moja has to agree with siostra in gender, number, and case.

• siostra is feminine singular
• so the possessive adjective is moja = my for a feminine singular noun

Compare:

• mój brat = my brother
• moja siostra = my sister
• moje dziecko = my child

So moja siostra is the correct matching form.

They are two forms of the same verb: woleć = to prefer.

Here the subject changes:

• moja siostra woli = my sister prefers
• ja wolę = I prefer

So:

• woli = he/she/it prefers
• wolę = I prefer

A few present-tense forms of woleć:

• ja wolę
• ty wolisz
• on/ona/ono woli
• my wolimy
• wy wolicie
• oni/one wolą

Because these nouns are the direct objects of woleć, and in Polish that usually means they go into the accusative case.

Their dictionary forms are:

• cukinia = zucchini
• kapusta = cabbage

But in the sentence they become:

• cukinię
• kapustę

This is a very common pattern for many feminine nouns ending in -a:

• nominative: -a
• accusative: -ę

For example:

• lubię kawę from kawa
• mam herbatę from herbata
• wolę kapustę from kapusta

Because they come after z meaning with, and in this meaning z requires the instrumental case.

So:

• ryż → ryżem
• makaron → makaronem

That is why we get:

• z ryżem = with rice
• z makaronem = with pasta

This is a very important pattern in Polish:

• z mlekiem = with milk
• z cukrem = with sugar
• z przyjacielem = with a friend

So in your sentence, z ryżem and z makaronem are both instrumental phrases.

Not always. It depends on the meaning.

• z + instrumental usually means with

  • z ryżem = with rice
  • z mamą = with mom

• z + genitive can mean from / off / out of

  • z domu = from the house
  • z Polski = from Poland

In this sentence, z clearly means with, so we use the instrumental:

• z ryżem
• z makaronem

Because a often links two ideas that are being contrasted.

Here the sentence compares two different people and their preferences:

• My sister prefers ...
• and/as for me, I prefer ...

So a works well because it has a slight contrastive feel, something like:

• whereas
• while
• and as for

By contrast, i is a more neutral and, used when you are simply adding information.

So:

• a ja wolę... = and I / whereas I prefer...

That is more natural here than i ja wolę...

Not strictly necessary, because the verb form wolę already tells you the subject is I.

So Polish could say:

• Moja siostra woli cukinię z ryżem, a wolę kapustę z makaronem.

But that sounds less natural here, because the sentence is explicitly contrasting my sister and me.

Using ja adds emphasis and makes the contrast clearer:

• a ja wolę... = but/as for me, I prefer...

Polish often drops subject pronouns, but keeps them when there is contrast, emphasis, or clarity.

Because Polish does not have articles like English a/an and the.

So Polish simply says:

• moja siostra
• cukinię
• kapustę

and the exact meaning depends on context.

English needs articles:

• my sister prefers the zucchini with rice
• my sister prefers zucchini with rice
• my sister prefers a zucchini dish with rice

Polish leaves that kind of distinction to context, word order, or extra words if needed.

Yes. Polish word order is more flexible than English because case endings show what each word is doing.

The neutral order here is very natural:

• Moja siostra woli cukinię z ryżem, a ja wolę kapustę z makaronem.

But other orders are possible for emphasis, for example:

• Cukinię z ryżem woli moja siostra, a ja wolę kapustę z makaronem.

That version emphasizes cukinię z ryżem more.

Still, for learners, the original word order is the best one to start with.

The letter ę is a nasal vowel, but in real speech its pronunciation can vary depending on position.

In these words:

• wolę
• cukinię
• kapustę

the final ę is often pronounced less strongly nasal than learners expect. In everyday speech, it may sound roughly like:

• wolę ≈ vo-leh / vo-len depending on speaker and speed
• kapustę ≈ ka-POOS-teh
• cukinię ≈ tsu-KEE-nyeh

The most important thing for a beginner is:

• recognize ę as a special Polish vowel
• do not replace it with a plain English ay
• listen to native recordings and imitate the rhythm

Even if your ę is not perfect at first, people will still understand you.

Here cukinię z ryżem functions as one food phrase: zucchini with rice.

So the structure is:

• woli [cukinię z ryżem]
• wolę [kapustę z makaronem]

In other words, z ryżem and z makaronem describe the foods being preferred, not the manner of preferring.

That is the natural reading of the sentence.