To celebrate the middle examination finished, mother and son go to Blockbuster to rent the films.
Son of No.1：「Mom, I want to rent “長江7號”.」
Son angrily ask：「Why?」
Mother：「Because it is a new film now, the price is 100 dollars per film, but, after couples of months, it will be treated as “old film” and price will be down to 60 dollars, so, for cost saving purpose, we should not rent it now.」
Son irritatingly yell：「You are so penny-pinching…………..」
Mother：「Um…….Am I??? Well, since how generous you are!!!... so, please donate your saving to rent “長江7號” for us.」