Humorous

I never thought it would come true so quickly, when my class teacher
told us a joke about future generation by his concept.
When I was in fourth grade, I heard that joke from my class teacher, just
seven years ago. I remember that day, after hearing that joke we all
laughed each other. I still haven't told about that joke, haven't!
I read that old job in the newspaper the previous day. "Bottle oxygen
like Bottle water", this was its title.
Our teacher made that joke while taking a lesson on air pollution in the
fourth grade environment studies. “In future generations, it might
have to pay for oxygen", it was not in such a sentence that the teacher
said then. I can't remember exactly that interesting passage. However, 
the idea was same. Anyway that joke has become a reality in less than a
decade.
"When some jokes become a reality, they bring us some sleepless nights..."