Thank you very much indeed for your last corrections!!

I still need your precious help to check a few more sentences.In particular, I would like you to tell me if the words in paranthes are also possible

1) The action takes place/happens,
occurs in ....(are they all OK?)
2) A character can be presented indirectly if the reader has to infer (derive?) the features of the character from his interaction with the other characters. If the presentation is direct the character tells the reader of (about?? which is better) his personality and appearance
3) Flat characters are easily recognizable since they are built (are based, revolve around?) a single psychological trait and their personality does not develop throughout the story (in the story, in the course of the story, within the story)
4)The narrator may be internal or external. The first .... the latter (is there a better sentence connector?)
5) The external narrator tells events he has not taken part in (he has not been involved in?)
6) The first-person narrator is identified with "I". The choice of this narrator has the function of bringing the reader close to the feelings of the narrator (of making him sympathize with his feelings..)and of limiting the reader's point of view.
7)A narrator can be obtrusive (intrusive?) if he makes personal remarks (comments?) on the society of his time and unobtrusiveif he shows (reports, tells) what happens without interfering with (in) the story.

1 - all are fine.

2 - "infer" is correct; "about" is correct in the second sentence.

3 - "based on a single..." and "in the story" are fine.

4 - "The former ... the latter" is the correct pairing of these terms. However, we speak of 1st-person narrator instead of internal, and 3rd-person instead of external.
http://web.cn.edu/kwheeler/lit_terms_P.html
Scroll down to POINT OF VIEW and read carefully.

5 - The 3rd-person narrator... (delete the words in parentheses).

6 - fine as is; delete the words in parentheses.

7 - Delete all words in parentheses except at the end; "in" is better than "with."

1) Yes, all three options are grammatically correct: "The action takes place," "The action happens," "The action occurs in..."

2) Both "infer" and "derive" are possible in this sentence, but "infer" is more commonly used. As for the preposition, "from" is the better choice, so it would be "infer the features of the character from his interaction with the other characters," and "direct the character tells the reader about his personality and appearance."

3) All options are possible in this sentence: "built on," "based on," "revolve around." For the second part, you can use any of these options: "throughout the story, in the story, in the course of the story, within the story."

4) Instead of "the first... the latter," you can use "the former... the latter."

5) Instead of "he has not taken part in," you can use "he has not been involved in."

6) Both "of bringing the reader close to the feelings of the narrator" and "of making him sympathize with his feelings" are correct options.

7) Both "obtrusive" and "intrusive" are possible in this sentence. As for the second part, you can use either "remarks" or "comments" to convey the same meaning. Similarly, you can use "interfering with" or "in" to describe the narrator's level of involvement in the story.