Okay closed!
Seems almost people thought the answer is more than one due to a sentence, "The number of correct answer is not necessarily only one.".
Well, I show the answer.
It is...
1. China
Yes, the country I have been to is only one
In my boyhood, I went to play baseball.
Ticket Holder :
Ritaka
Oh! ticket holder is only one too!
You are lucky guy Ritaka
Don't worry, other guys. I'll open next round as soon as I can. (maybe in a few hours or more.)
At next round, I'll try to make better question. (it has only one correct answer but it has many choices.)
And also I'll invite an awesome guest! Expect it!