Minha irmã prefere andar de moto quando a avenida está vazia.

Because irmã is a feminine noun, so the possessive must agree with it.

• minha = my for a feminine singular noun
• meu = my for a masculine singular noun

Examples:

• minha irmã = my sister
• meu irmão = my brother

So the possessive agrees with the thing possessed, not with the speaker.

The ã shows a nasal vowel, which is very common in Portuguese. So irmã is not pronounced like a plain a sound. The vowel is nasalized.

Also, irmã is the feminine form of irmão:

• irmã = sister
• irmão = brother

This is a useful pair to memorize together.

This is a very common structure in Portuguese.

• prefere = prefers
• andar = to ride / to go / to travel depending on context

After preferir, Portuguese often uses an infinitive verb, just like English does in sentences such as she prefers to ride.

So:

• prefere andar de moto = prefers to ride a motorcycle / prefers going by motorcycle

Other examples:

• Eu prefiro estudar à noite. = I prefer to study at night.
• Ela prefere ficar em casa. = She prefers to stay home.

Not exactly. Andar can mean different things depending on context.

It can mean:

• to walk
• to go around / move around
• in expressions like andar de + vehicle, it means to go by / ride

So:

• andar alone often suggests walking or moving around
• andar de moto means to ride a motorcycle / go by motorcycle

Similar expressions:

• andar de carro = to go by car / drive around
• andar de ônibus = to go by bus
• andar de bicicleta = to ride a bicycle

Because andar de + vehicle is the usual way to express traveling by a means of transportation.

• andar de moto = to ride a motorcycle / go by motorcycle

Other prepositions would change the meaning:

• na moto can mean on the motorcycle, emphasizing physical position
• com moto would sound like with a motorcycle, which is not the normal way to express transportation here

So in this sentence, de is the natural choice.

Portuguese often uses the definite article more often than English does.

So a avenida literally means the avenue, but in many contexts English would simply say the street or leave article usage more flexible. In Portuguese, using the article here sounds normal and natural.

This happens a lot:

• o carro = the car
• a escola = the school
• a minha irmã / minha irmã = my sister

In this sentence, a avenida refers to the avenue/street in a general but definite way, so the article sounds very natural.

Because estar is usually used for conditions or states, while ser is used more for identity, essence, or permanent characteristics.

Here, the avenue being empty is a temporary condition:

• a avenida está vazia = the avenue is empty

If you said é vazia, it could suggest that being empty is more of a defining characteristic, which sounds less natural in this context.

This is a classic ser vs. estar distinction:

• A rua está vazia agora. = The street is empty now.
• A cidade é tranquila. = The city is calm/quiet by nature.

Because adjectives usually agree in gender and number with the noun they describe.

• avenida is feminine singular
• so the adjective must also be feminine singular: vazia

Compare:

• o carro está vazio = the car is empty
• a avenida está vazia = the avenue is empty
• as ruas estão vazias = the streets are empty

This kind of agreement is very important in Portuguese.

Because the subject is singular: a avenida.

• a avenida = singular
• therefore está = singular

Compare:

• A avenida está vazia. = The avenue is empty.
• As avenidas estão vazias. = The avenues are empty.

Notice that both the verb and the adjective change in the plural sentence:

• está → estão
• vazia → vazias

Because Portuguese often uses the present tense after quando when talking about something habitual, general, or expected.

In this sentence, it describes a usual situation:

• Minha irmã prefere andar de moto quando a avenida está vazia.
• She prefers riding when the avenue is empty.

This is not necessarily about one specific future event. It sounds like a general preference or repeated situation.

If the sentence were about the future, Portuguese often uses the future subjunctive after quando:

• quando a avenida estiver vazia = when the avenue is empty / when the avenue becomes empty

So:

• quando ... está = when it is / whenever it is
• quando ... estiver = when it is, in the future

Yes. Both are possible in Brazilian Portuguese.

• Minha irmã
• A minha irmã

In Brazil, possessives can appear with or without the definite article, depending on region, style, and preference. In many contexts, both sound natural.

Very roughly:

• minha irmã is very common and straightforward
• a minha irmã can sound a little more explicit or natural in some varieties

So the sentence could also be:

• A minha irmã prefere andar de moto quando a avenida está vazia.

The basic structure is:

• Minha irmã = subject
• prefere = main verb
• andar de moto = infinitive phrase/complement
• quando a avenida está vazia = time clause

So the pattern is roughly:

Subject + verb + infinitive phrase + quando-clause

Portuguese word order here is very similar to English, which makes this sentence fairly learner-friendly.

Not exactly. Avenida usually means avenue, and it often suggests a broader or more important road than a small street.

So:

• avenida = avenue
• rua = street

Depending on the context, English translations may vary, but the Portuguese word specifically is avenida.

You would need to change the possessive, the noun if necessary, and the verb.

For example:

• Minhas irmãs preferem andar de moto quando a avenida está vazia.

Changes:

• minha → minhas
• irmã → irmãs
• prefere → preferem

The second clause stays singular because a avenida is still singular.

If that part were plural too:

• Minhas irmãs preferem andar de moto quando as avenidas estão vazias.

It is natural and grammatically correct. It sounds like a normal statement about someone’s preference.

A Brazilian speaker might also say similar versions such as:

• Minha irmã gosta de andar de moto quando a avenida está vazia.
• Minha irmã prefere andar de moto quando a rua está vazia.

But the original sentence is perfectly normal and idiomatic.