jeonghwa hwaldongui gyeolgwaga daedanhaessseupnida.

A very literal breakdown is:

• 정화 활동의 = of the cleanup/purification activity
• 결과가 = the result(s)
  • subject marker
• 대단했습니다 = was/were impressive / great / remarkable

So the sentence structure is basically:

[Noun phrase] + [subject] + [description]

More literally: As for the results of the cleanup activity, they were remarkable.

A natural English translation would often be: The results of the cleanup activity were impressive.

의 usually shows a relationship similar to of or 's in English.

So:

• 정화 활동 = cleanup activity / purification activity
• 정화 활동의 결과 = the result(s) of the cleanup activity

You can think of it as linking two nouns:

• A의 B = B of A / A's B

Here, 결과 belongs to or comes from 정화 활동, so 의 is used.

This is a very common learner question.

• 가/이 marks the grammatical subject.
• 는/은 marks the topic and often adds contrast or emphasis.

In 결과가 대단했습니다, the speaker is presenting the result(s) as the thing being described:
The results were impressive.

If you changed it to 결과는 대단했습니다, it would sound more like: As for the results, they were impressive
possibly with a contrastive nuance, such as:

• the process was difficult, but the results were impressive
• other things were ordinary, but the results were impressive

So 가 is the more neutral choice here.

It can be either, depending on context.

Korean often does not mark singular vs. plural as clearly as English does. So 결과가 could mean:

• the result was
• the results were

In English, this sentence is often translated as The results were impressive, because that sounds natural in many contexts. But the Korean itself does not force that interpretation.

정화 means something like purification, cleanup, or restoration, depending on context.
활동 means activity.

So 정화 활동 could mean things like:

• an environmental cleanup activity
• a purification effort
• a restoration activity

In many real-life contexts, especially environmental ones, it often suggests something like cleanup work or cleanup activities.

The most natural English meaning depends on the situation.

대단하다 means to be great, impressive, remarkable, extraordinary.

So 대단했습니다 is the past formal-polite form:

• 대단하다 = to be impressive / remarkable
• 대단했습니다 = was/were impressive / remarkable

It does not necessarily mean only big or huge. It often expresses admiration, like:

• That was amazing
• That was impressive
• That was remarkable

In this sentence, it means the result(s) were notably good or striking.

In Korean, words that function like adjectives in English are often called descriptive verbs.

So 대단하다 behaves grammatically like a verb in many ways, even though it translates like an adjective:

• English: The results were impressive
• Korean: 결과가 대단했습니다

This is very normal in Korean. Other common examples are:

• 크다 = to be big
• 작다 = to be small
• 좋다 = to be good

So even though 대단했습니다 means something adjective-like in English, its Korean grammar follows verb-style conjugation.

Because -했습니다 is a past formal ending.

• 대단합니다 = is impressive / are impressive
• 대단했습니다 = was impressive / were impressive

The speaker is talking about the result as something already observed or evaluated, so the past tense is natural.

For example:

• after the activity finished
• after seeing the outcome
• when reporting on what happened

It is formal and polite.

The ending -습니다 / -했습니다 is commonly used in:

• presentations
• reports
• speeches
• news-style writing
• formal announcements

So 정화 활동의 결과가 대단했습니다 sounds appropriate in a formal report or presentation.

A less formal polite version would be:

• 정화 활동의 결과가 대단했어요.

A plain casual version might be:

• 정화 활동의 결과가 대단했어.

Sometimes, yes, depending on style and context.

You may also hear or see:

• 정화 활동 결과가 대단했습니다

Korean sometimes omits 의 when noun relationships are clear, especially in compounds or formal writing. However:

• 정화 활동의 결과 is very clear and standard
• 정화 활동 결과 can sound a bit more compact or report-like

For learners, keeping 의 is often safer until you get used to when omission sounds natural.

Yes, in a sense.

Korean very often leaves out anything that is already clear from context. In this sentence, there is no separate word for it or they because 결과가 already tells us what is being described.

So instead of saying something like:

• The results, they were impressive

Korean simply says:

• 결과가 대단했습니다

This is normal and natural.

A careful learner-friendly pronunciation would be close to:

정화 활동의 결과가 대단했습니다
→ 정화 활똥에 결과가 대단핻씀니다

A few helpful notes:

• 활동 is pronounced more like 활똥
• 의 in this kind of phrase is often pronounced like 에
• 했습니다 is commonly heard like 핻씀니다

You do not need to pronounce every letter exactly as written in a spelling-based way. Natural Korean pronunciation often changes sounds between syllables.

Not exactly.

The Korean sentence specifically says that the result(s) of the activity were impressive:

• 정화 활동이 대단했습니다 = The cleanup activity itself was impressive
• 정화 활동의 결과가 대단했습니다 = The result(s) of the cleanup activity were impressive

So 결과 is important. It shifts the focus from the activity itself to what came out of it.