jihacheoreseoneun inteones yeongyeori jal an doeneun dega isseo.

On the subway, there are places where the internet connection doesn’t work well.

Breakdown of jihacheoreseoneun inteones yeongyeori jal an doeneun dega isseo.

• ~이: subject particle
• ~에서: location particle
• ~는: topic particle
• ~가: subject particle

Questions & Answers about jihacheoreseoneun inteones yeongyeori jal an doeneun dega isseo.

What does 지하철에서는 mean, and why is it 에서는 instead of just 에서?

지하철에서 means in/on the subway (location where something happens).
Adding -는 → 지하철에서는 adds a topic/contrast nuance:

• 지하철에서는 = as for on the subway / when it comes to the subway (at least there)
  It often implies comparison, like: On the subway, (but maybe not elsewhere)...

So the sentence feels like: On the subway, there are places where the internet connection doesn’t work well.

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Why is 인터넷 연결이 marked with 이/가?

이/가 marks the grammatical subject of the clause 잘 안 되는 (doesn’t work well).

• 인터넷 연결이 잘 안 되다 = the internet connection doesn’t work well
• Here, that whole idea becomes a modifier describing 데 (places).

If you used 은/는 instead (인터넷 연결은), it would shift toward a broader topic/contrast about internet connection in general, and it can sound less natural in this specific structure.

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How should I understand 잘 안 되는? Is it “not good,” “not possible,” or “not working”?