Mr Brown was going away for a week. Before he left, he said to his son, "if anyone asks for me, you can tell him that your father has been out for doing something, and will be back in a week, then be sure to ask him to sit down for a cup of tea."
"OK, Dad," said his son. But he was afraid his son couldn’t remember this, he wrote these words down on a piece of paper and gave it to him. His son put it into his small pocket, took it out and looked at it every now and then.
Four days passed, but no one came to see his father. The boy thought that there was no man to come and that the piece of paper was of no more use for him, so he burnt it that evening.
The next afternoon, someone knocked at the door. The boy opened it. A man was standing at the door and said, "Where is your father?" The boy put his hand into his pocket at once and looked for the piece of paper. He could not find it. He suddenly remembered he had burnt it, so he shouted, "No more."
The man was very surprised. He asked, "No more? I met your father last week. When did it happen?"
"Burnt yesterday evening."

对于不同的x，下列关于年龄的统计量不会发生改变的是（   ）

                                                                      Winners Club
   Winners Club is a bank account (账户) specially for teenagers. It has been sep up to help you better manage your money. The club is a bank account where you receive a key-card, so you can enjoy dealing with your money 24/7 — that's 24 hours a day, 7 days a week!
Here are the features (特点) of the club.
                                                     No account keeping fees (费用)!
   You're not a rich man, so we don't expect you to pay large fees. In fact, it's free for all the service!
                                                     Excellent interest rates (利率)!
   You want your money to grow, right? If you put money into the club without taking it out for a year, the club will give you a good rate of interest.
                                                             Convenient (方便)！
   Teenagers are busy — we get that. You may never need to come to a bank at all. With the club you can choose to use handy tellers and to bank from home using the phone and the Internet. This could be your pocket money or your pay from your part-time job!
                                                   A free magazine included！
   Besides your account report, you will receive a free magazine full of good ideas about making more money. There are also other fantastic offers only for the club members.
                                                         Easy to be a member！
   It is so easy to join. Simply fill in an application form (申请表). By the way, one of your parents must agree on it. Then you can become a member of the club.
   Now you see the club is a great choice for teenagers. We can't wait to have you as a Winners Club member.