bangi neomu dapdaphaeseo changmuneul yeoreosseoyo.

Here, 답답하다 means stuffy, airless, or oppressive—the feeling you get when a room needs fresh air.

This word is also used for emotions, where it can mean frustrated, constricted, or uneasy, but in this sentence it is clearly the physical meaning: the room felt stuffy.

이/가 marks the subject, while 을/를 marks the object.

In this sentence, the room is the thing that is stuffy, so 방이 is the subject of 답답하다:

• 방이 답답하다 = The room is stuffy

If you said 방을, it would sound like the room is receiving an action, which is not what is happening here.

Both can work, but the nuance is a little different.

• 방이 너무 답답해서... focuses on the room as the thing that is stuffy.
• 방은 너무 답답해서... would make the room more of a topic, sometimes with a slight contrastive feeling, like As for the room, it was so stuffy...

In a simple sentence like this, 이/가 is very natural because it just states the condition directly.

Literally, 너무 often means too or excessively.

But in everyday Korean, people very often use 너무 more loosely to mean so, really, or very, even when they do not mean something is excessive in a strict sense.

So here it can feel like:

• The room was too stuffy
• The room was so stuffy
• The room was really stuffy

All are reasonable depending on the translation style.

답답해서 is 답답하다 plus the connective ending -아서/어서, which often means because, so, or and so.

Breakdown:

• 답답하- = stem of 답답하다
• -아서/어서 = linking ending
• 답답해서 = because it was stuffy / it was stuffy, so...

So the sentence structure is:

• 방이 너무 답답해서 = because the room was so stuffy
• 창문을 열었어요 = I opened the window

This is because of how 하다-type words combine with -아/어서.

With 하다, -아/어서 usually becomes -해서:

• 답답하다 → 답답해서
• 공부하다 → 공부해서
• 운동하다 → 운동해서

So 답답해서 is the normal contracted form.

Korean often leaves out subjects like I, you, or we when they are obvious from context.

In English, you usually need to say I opened the window.
In Korean, if it is clear who did it, you can just say:

• 창문을 열었어요

So the full sense is understood as something like:

• (I) opened the window

That is the normal Korean sentence pattern.

Korean usually puts background information, reasons, or conditions before the main action:

• 방이 너무 답답해서 = because the room was stuffy
• 창문을 열었어요 = opened the window

So Korean often builds toward the main verb at the end. This is very common and natural.

창문 means window, and 을 is the object particle.

So 창문을 열었어요 means opened the window.

Also, Korean does not have articles like a or the, so 창문 by itself can mean:

• a window
• the window

The exact meaning depends on context. In this sentence, English usually translates it as the window.

It comes from the dictionary form 열다 (to open).

Breakdown:

• 열다 = to open
• 열었- = past tense stem
• -어요 = polite ending

So 열었어요 means opened or I opened in polite speech.

It is a standard polite past-tense form.

It could be a separate sentence:

• 방이 너무 답답했어요. 창문을 열었어요.
  The room was very stuffy. I opened the window.

But when Korean connects the reason directly with -아서/어서, it usually uses the descriptive form:

• 방이 너무 답답해서 창문을 열었어요

This is the most natural way to say Because the room was stuffy, I opened the window.

Yes. In English, you might translate it either way depending on what sounds natural.

So this sentence can be understood as:

• Because the room was so stuffy, I opened the window.
• The room was so stuffy, so I opened the window.

In Korean, -아서/어서 links the first clause to the second and often shows a natural reason-result relationship.