"Sorry, I can't go to the US with you."
Things I don't really understand about this: 1. 能 vs. 可以 - would 可以 really be wrong?, and 2. 一起 - is this actually needed here?
OK, so apparently it wants 能 instead of 可以, but it doesn't really care about 一起.
能 vs 可以 I was taught that the the first is 'able to' the secone is 'can' I believe you can use both of them in this sentence, but one would have a more formal tone