I left out the following sentences. Thank you very much.
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. He helped sick people with medicine (no plural) from the plane.
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?
5) I watched Lost but after a quarter of an hour I fell asleep.
6) Did you see (or watch since it is on TV) the last episode of "Lost"?
No, I missed it. I was visiting my sister.
7) When is the next episode (can you say that?) Next Monday. Make sure you'll watch it. I will.