"Ĉar" vs "Pro"
Which is the right answer to "kial"? "Ĉar", "Pro", both, or another one? Is any difference between them?
I agree with amuzulo. Ĉar introduces a sub-clause that shows a cause, reason or motive. You could also say: ĉar = pro tio, ke. Pro is a preposition. It does indeed mean because of, on account of, for the sake of, due to. If you get a question that starts with kial, in most cases you should expect a sub-clause in the answer. e.g. Kial la vetero estas malvarma? La vetero malvarmas, ĉar la vento estas tre forta (or).....la vetero malvarmas pro la forta vento. I hope that this makes sense.