Mi hermana prepara zumo de pomelo algunos domingos.

Because mi without an accent is the possessive adjective meaning my.

• mi hermana = my sister

With an accent, mí is a pronoun meaning me after a preposition:

• para mí = for me
• a mí = to me

So in this sentence, mi is correct because it shows possession.

Prepara is the third person singular form of the verb preparar in the present indicative.

That matches mi hermana, which is:

• third person
• singular

So:

• yo preparo = I prepare
• tú preparas = you prepare
• él/ella prepara = he/she prepares

Since mi hermana means my sister, the verb must be prepara.

Spanish often uses the present tense for habitual or repeated actions, just like English does in sentences such as My sister makes grapefruit juice on some Sundays.

Here, prepara does not mean she is doing it right now. It means this is something she sometimes does.

The phrase algunos domingos gives the habitual meaning:

• on some Sundays
• some Sundays

So the sentence describes a recurring action, not a one-time event.

In Spanish, when talking about something in a general, indefinite way, the article is often omitted.

So:

• prepara zumo de pomelo = she makes grapefruit juice

This sounds natural because it refers to some grapefruit juice, not a specific previously mentioned juice.

If you said prepara el zumo de pomelo, that would usually mean the grapefruit juice—a specific one already known in the conversation.

Because the sentence is in Spanish from Spain, and in Spain zumo is the usual word for juice, especially fruit juice.

• zumo de naranja = orange juice
• zumo de pomelo = grapefruit juice

In much of Latin America, jugo is more common for juice.

So both may be understood, but for Spain, zumo is the most natural choice.

Spanish often uses de to show what something is made from or consists of.

So:

• zumo de pomelo = grapefruit juice
• literally: juice of grapefruit

This is the normal structure in Spanish:

• zumo de naranja = orange juice
• zumo de limón = lemon juice
• tarta de queso = cheesecake

English often puts one noun directly before another, but Spanish usually uses de.

Algunos domingos means some Sundays.

It suggests that the action happens:

• occasionally
• on certain Sundays
• not every Sunday

It does not mean one particular Sunday. It refers to repeated occasions.

Compare:

• los domingos = on Sundays / every Sunday / Sundays in general
• algunos domingos = on some Sundays
• este domingo = this Sunday

Because the sentence refers to more than one Sunday over time.

• algunos domingos = some Sundays

If it were singular, algún domingo, it would usually mean some Sunday in the sense of one Sunday, at some point.

So the plural is important because it shows a repeated habit.

In Spanish, expressions of time like days of the week often appear without a preposition where English uses on.

So Spanish says:

• algunos domingos
• literally: some Sundays

But English translates it as:

• on some Sundays

This is normal in Spanish. Other examples:

• los lunes trabajo = I work on Mondays
• el martes salimos = we’re going out on Tuesday

Yes. Spanish word order is fairly flexible, especially with time expressions.

The original sentence:

• Mi hermana prepara zumo de pomelo algunos domingos.

You could also say:

• Algunos domingos, mi hermana prepara zumo de pomelo.

Both are natural. The second version puts more focus on when it happens.

The original order is neutral and very common:

• subject + verb + object + time expression

Yes, you often can.

• prepara zumo de pomelo = she prepares/makes grapefruit juice
• hace zumo de pomelo = she makes grapefruit juice

In many contexts, both sound natural. Preparar can suggest preparing something a bit more explicitly, while hacer is the very common general verb to make/do.

So this sentence uses prepara naturally, but hace would also be possible in everyday Spanish.

In standard Peninsular Spanish, a rough pronunciation is:

• zumo ≈ THOO-mo
• de ≈ deh
• pomelo ≈ poh-MEH-lo

A few useful points for Spain:

• z in zumo is pronounced like the th in thin in much of Spain
• u is a pure vowel, like oo
• j does not appear here, so there is no strong h-like sound in this sentence

So the whole phrase is roughly:

• THOO-mo deh poh-MEH-lo

In modern everyday Spanish, especially in Spain, pomelo normally means grapefruit.

So:

• zumo de pomelo = grapefruit juice

You may sometimes see botanical distinctions in technical contexts, but for ordinary learners and everyday speech, pomelo is the normal word to understand here as grapefruit.