Nó không những khỏe mà còn được thả về tự nhiên.

It means not only ... but also ....

So in this sentence:

• Nó không những khỏe = It is not only healthy / strong
• mà còn được thả về tự nhiên = but was also released back into nature / into the wild

This is a very common Vietnamese pattern for adding a second, often stronger or more important, point.

You may also see:

• không chỉ ... mà còn ...
• không những ... mà còn ...

These are very similar in meaning.

Nó is a third-person pronoun, but it does not work exactly like English he/she/it.

In this sentence, nó most naturally means:

• it for an animal
• sometimes he/she for a child or a person, depending on context and relationship

Important nuance:

• For animals, nó is very common and neutral.
• For people, nó can sound rude, distant, or only appropriate in certain family/social contexts.

Since the sentence talks about being released back into nature, nó probably refers to an animal.

Khỏe can mean several related things:

• healthy
• well
• strong
• in good condition

In this sentence, khỏe most likely means the animal is healthy enough / recovered enough to be released.

So depending on context, English could render it as:

• healthy
• well
• strong
• in good condition

Vietnamese often uses khỏe a bit more broadly than English uses just healthy.

Here, được marks a kind of passive meaning.

• được thả = was released
• literally something like got released

So:

• được thả về tự nhiên = was released back into nature

In Vietnamese, được often suggests that something happened to the subject, and it can sometimes carry a positive or favorable sense. Here it is mainly functioning as a passive marker.

Compare:

• Nó được thả về tự nhiên. = It was released into the wild.

Without được, the sentence would sound different and less clearly passive.

Because thả by itself usually means to release / let go, and it normally needs an agent or a clearer active structure.

For example:

• Người ta thả nó về tự nhiên. = People released it into the wild.

If you want the animal to be the subject of the sentence, Vietnamese commonly uses được:

• Nó được thả về tự nhiên. = It was released into the wild.

So được helps shift the sentence into a passive-like structure.

Yes, literally it is something like back to nature, but in natural English it usually means:

• into the wild
• back into nature
• back to its natural habitat (depending on context)

Breakdown:

• về = to / back to / return to
• tự nhiên = nature / natural environment

So thả về tự nhiên is a natural Vietnamese way to say an animal is released back where it belongs.

Yes. That would sound a bit more explicit or formal.

Compare:

• thả về tự nhiên = more natural and concise
• thả về môi trường tự nhiên = release back into the natural environment

You might also hear:

• thả về rừng = release into the forest
• thả về biển = release into the sea
• thả về môi trường sống tự nhiên = release back into its natural habitat

The original sentence is short and natural.

Because the full correlative structure is:

• không những A mà còn B = not only A but also B

Here:

• A = khỏe
• B = được thả về tự nhiên

So the sentence is built as:

• Nó không những khỏe mà còn được thả về tự nhiên.

This pattern links two pieces of information and emphasizes that the second one adds to the first.

Yes. That is very common.

You can say:

• Nó không chỉ khỏe mà còn được thả về tự nhiên.

This means basically the same thing: It is not only healthy, but was also released back into nature.

In everyday Vietnamese, không chỉ ... mà còn ... is often slightly more common in conversation, but both are correct.

Vietnamese verbs do not change form for tense the way English verbs do.

So được thả by itself does not automatically tell you whether it is:

• being released
• has been released
• was released

The time is understood from context.

In this sentence, because of the meaning, English will often translate it as past:

• It was not only healthy, but was also released back into nature.

But if the surrounding context were different, another tense might be possible.

Vietnamese often relies on context or time words such as:

• đã = past/completed
• đang = ongoing
• sẽ = future

For example:

• Nó đã được thả về tự nhiên. = It was / has been released back into nature.

Yes, but the nuance changes slightly.

• khỏe = healthy, well, strong
• khỏe mạnh = healthy and strong; a bit fuller or more emphatic

So:

• Nó không những khỏe mà còn được thả về tự nhiên.
• Nó không những khỏe mạnh mà còn được thả về tự nhiên.

Both are fine, but khỏe is simpler and very natural. In many contexts, just khỏe is enough.

Yes, it is natural and grammatically correct.

It sounds like something you might read in:

• a news report
• a rescue update
• a conservation story
• a social media post about an animal recovery

It has a slightly written or informative tone because of the structure không những ... mà còn .... In casual speech, someone might also say something simpler, such as:

• Nó khỏe rồi, lại còn được thả về tự nhiên nữa.

But the original sentence is perfectly good standard Vietnamese.

The sentence is highlighting two positive outcomes:

1. Nó khỏe — the animal is healthy / recovered.
2. Nó được thả về tự nhiên — it was released back into the wild.

Using không những ... mà còn ... makes the second point feel like an added success.

So the tone is something like:

• It wasn’t just healthy — it was even released back into nature.

That structure gives the sentence a sense of good news or successful progress.