Student or Learner
It is hard to say if I'd choose to live in either the city or the country because I can't say which is distinctly better.
If I have to choose one, I would say I prefer living in the city.
I'd say that because I've always lived in the city even though I dream to live in the countryside someday.
Q1) I wonder if I need to change 'the' underlined should change to an article a.
Q2) Is there any other errors or unnatural structures in those three sentences?
"The" in this case carries an indefinite meaning – you're referring to living in a city, city being a habitiat. If you were to say a city, that would be saying a specific city and the country means in the countryside and a country means a country such as England, France etc.
You're sentences, by the way, are perfect.
[Not a teacher]