Comment comprendre « devoir » en conditionnel - Si le train était à l'heure, ils arriveraient à 12h15. - Si le train était à l'heure, ils devraient arriver à 12h15. Est-ce que toutes les deux phrases sont juste? Pour la première phrase, disons que il est 12:00 maintenant, mais on est informé que le train, qui devra arriver à 12:15, est en retard, dans ce cas, on dit: « Si le train était à l'heure, ils arriveraient à 12h15. » C’est à dire, ce train devra arriver à 12:15 mais on n’est pas sûr maintenant. Est-ce que je suis juste? Si oui, comment on peut comprendre la deuxième phrase?

"if I was" or "if I were" As my understanding, "if I were" means that it can't be true. For example, If I were you, I would study French. We use "if I were you", because I can't be you in any case, it can't be true definitely. Well, I can't distinguish "if I were" and "if I was". If I were you, I would go shopping tomorrow. (Currently the listener hasn't decided if he would go shopping or not) If I were you, I would have gone shopping yesterday. (Currently the fact that the listener hasn't gone shopping has happened.) If I was wrong, I would be sorry. (Currently I'm not sure if I was wrong or not) If I were wrong, I would have been sorry. (Currently I have known that I was right, the fact that I was wrong hasn't happened). Am I right about the understanding of these four sentences? Furthermore, I'm not sure the sentence "If I were you, I would go shopping tomorrow." is correct, should I say "If I were you, I would go shopping tomorrow." or "If I was you, I would go shopping tomorrow."?

"il est" ou "c'est" Disons que je suis en train de parler avec queleuq'un, je veux présenter une personne, qui n'est pas avec nous, c'est-à-dire, la personne qui je veux présenter n'est pas devant nous deux. Alors, je dois dire "Il s'appelle Titi, Il est mon ami" ou bien "Il s'appelle Titi, c'est mon ami"?

Which is more natural？ 1.I shouldn't have lied to her at first. 2.I shouldn't have lied to her in the first place.

What's the difference between SINCE and BECAUSE？ What's the difference when they are used to give the reason for something？

Why use SPEAK rather than TALK？ We had a little quarrel one day last month，and after that day，we did not SPEAK to each other for a whole week.

How do we understand this sentence "I co-wrote, acted, sang and danced in an original musical comedy produced by the Associated Students. It played in the largest auditorium to standing-root-only houses." I can not understand what "It played in the largest auditorium to standing-root-only houses" means, especially this "to".