Greencard

Yes, I am a greencard holder, and it will be expired in December.
So...here is what I need to think about...
Would I want to renew it for another 10 years?
Would I go ahead get a citizenship?
To me, it is a big decision to make since Japanese government won't let me keep both citizenship. More than likely, I have to let my Japanese citizenship go.
Extra spending...it will cost me about $500.00 to apply...
I don't think we will ever move back to Japan...so I think I need to go ahead get one.