1, not only〜 but... の意味
〜だけでなくまた...
(Not only children but many grown-ups enjoy reading) comic magazines.
2, It's hard to believe thatの意味
そんなことはとても信じられない
It's(hard to believe that she is)eighty.
3, Either you or I〜の意味
あなたか私のどちらかが〜
(Either you or I must go)there at once.