I included the sentences I was most doubtful about. Thank you.
1) In each episode there was a flashback, which showed what the characters were doing before the crash. Through the flashbacks (?) the audience learned more about the characters (could learn more about the characters).
2) A really interesting character was the American doctor Jack interpreted (played) by Matthew Fox.
3) The island, however, kept its mystery till the series ended in 2010.
4) What was on Channel five last night?
What did you watch on TV last night?
Was there anything interesting on TV last night? I watched Lost but after a quarter of an hour I fell asleep.
5) Did you see (or watch since it is on TV) the last episode of "Lost"?
When is the next episode of Lost? (can you say that?)
All looks good, including the alternatives in the last one. Add commas and delete things in parentheses in the earlier sentences.
1) In each episode of "Lost," there were flashbacks that depicted what the characters were doing before the crash. By watching these flashbacks, the audience could learn more about the characters.
To answer your question, the sentence can be revised as follows: Through the use of flashbacks, the audience could learn more about the characters in each episode of "Lost."
2) One of the captivating characters in "Lost" was the American doctor Jack, portrayed by Matthew Fox.
3) The island, however, remained mysterious until the series concluded in 2010.
4) To find out what was on Channel five last night, you can check the TV schedule or program guide for that channel. Alternatively, you can search online or use a TV listings app to see what aired on that specific channel.
Regarding the question about what you watched on TV last night, you mentioned that you watched "Lost," but fell asleep after about fifteen minutes.
If you want to know if there was anything interesting on TV last night, you can refer to TV listings or ask someone who might have watched TV during that time.
5) To determine if someone has seen the last episode of "Lost," you can ask, "Did you see the final episode of 'Lost'?" Alternatively, you could ask, "Did you watch the last episode of 'Lost' on TV?"
As for when the next episode of "Lost" would air, it depends on the context of the conversation. If the series has already ended, there won't be any new episodes. However, if the series is currently airing or has upcoming episodes, you can inquire about the next episode by asking, "When is the next episode of 'Lost'?"