Well, Number 6, I'm not saying that's impossible...

But it's not too likely. Would they not have to go through eastern Russia first? Would the Russians let them?

I suppose anything's possible eventually, if one waits long enough. The Chinese would need to dominate the Pacific Ocean to effectively invade North America. That would require them having the world's pre-eminent navy, and that is something they are nowhere even near having at this point. The biggest navy is that of the USA, with Russia coming next.

I've studied my WWII history, and I know what it takes to mount an across the ocean invasion of a continental power. Only the USA and Great Britain have possessed such a capability in the last 100 years.

Hitler couldn't manage it across the little strip of water called the English Channel...and he would have if he could have.