11 화병을 닦은 사람은* 누구입니까? 12 화병을 닦은 사람이* 누구입니까? Both can work. But more importantly, think about "Who cleaned the vase?". For that, only 누가 화병을 닦았습니까? works. This is one of the "must" cases which are more important for new learners. 13 자동차에 있는 동물은* 무엇입까? 14 자동차에 있는 동물이* 무엇입까? Both can work. #13 seems better. Again, 무엇이 자동차 안에 있슴니까? works while 무엇은 자동차 안에 있습니까? is nonsense. 15 철수는* 학교(에) 걸어갑니다. (걸러갑니다 -> 걸어갑니다) 16 철수가* 학교(에) 걸어갑니다. #15 can be a general statement (철수 always goes to school on foot) or a remark during a discourse about him. #16 can only be a factual statement of what's happening right now. 17 경숙은* 친구를 기다립니다. 18 경숙이* 친구를 기다립니다. Both can work. 19 집 앞에 있는 나무는* 크지 않습니다. 20 집 앞에 있는 나무가* 크지 않습니다. #19 is more natural because 크지 않습니다 is an unchanging attribute which works better with 는. #20 sounds strange. Also consider these similar sentences: 21 집 앞에 있는 나무는 잘려 버렸더라고요. (I see that the tree in the front has been cut) 22 집 앞에 있는 나무가 잘려 버렸더라고요. Now #22 is more natural because it is about an incidental fact. #21 is also okay. 23 그 여자는* 오늘 아침 일찍 일어났습니다. 24 그 여자가* 오늘 아침 일찍 일어났습니다. #23 sounds natural and #24 doesn't, because 오늘 일찍 일어났습니다 is an entirely personal thing with no connection to anything else. It is only relevant while relating things about 그 여자, so 은 is appropriate. On the other hand, if the fact had a relevance to the outside world, 그 여자가 would be okay, as in 그여자가 철수를 학교에 데려갔습니다 (She took 철수 to school). Again, some of them are too subtle to differentiate. I would recommend concentrating on more distinctive examples. Anyway, feel free to ask again if you'd like to know more about any of them.

Some examples are hard to explain because they are all short, isolated sentences. The 은/는, 이/가 distinction is more pronounced and easier to explain when the sentences are in context. Also, what's more important for learners is knowing the clear cut cases where only one and not the other makes sense. In many situations, either particle may work fine with a subtle nuance difference which might be too minute to understand. Anyway, I'll try to explain it as best as I could, using some code phrases below. - For 은/는: 1. general statement (representative of the whole group) 2. set it apart from the other(s). - For 이/가: 1. factual and incidental 2. designate one instance out of indeterminate many. 1 역에 사람이* 옵니다. 2 역에 사람은* 옵니다. #1 makes a factual statement making a designation of a specific person, that a person comes to a station. #2 is strange. 사람은 역에 옵니다 is more common ordering, but even as such 은 implies a general statement which is at odds with 역에 옵니다, a clearly incidental statement. 3 오랜지는* 먹고 바나나는* 먹지 않았습니다. 4 오랜지를* 먹고 바나나를* 먹지 않았습니다 #3 is more natural as 는 sets the two apart, like "As for oranges I ate them, but not the bananas". #4 sounds monotonous and mechanical, like "I ate the oranges and I didn't eat the bananas". 5 구두가* 자동차 안에 있습니다. 6 구두는* 자동차 안에 있습니다. Both can work. #5 seems better. 7 아파트는* 높고 집은 낮습니다. 8 아파트가* 높고 집은 낮습니다. Both can work. #7 seems better. 9 닭과 개는* 동물 입니까? 10 닭과 개가* 동물 입니까? Both can work. #9 seems better. (continued)