One day，Daniel and his uncle Bob went to the store together．Uncle Bob gave Daniel a one—dollar bill and told him he could buy(无论什么)he wanted with that money. Daniel picked out two chocolate candy bars which cost(五十)cents each．
As they were(离开)，his uncle said that when he was a (孩子)he was able to buy five candy bars with one dollar．This was because back then，they only cost 20 cents each．Daniel became (惊奇的)．
"You see，Daniel，the(价格)of all things usually goes up as time goes by．That's why one dollar earned today is more valuable than one dollar earned one year later．This is called the Time Value of Money．Do you understand?" "Not really，"Daniel replied(快地)．
"Look at the candy bars in your(手)．When l was a kid，I could buy five of them with one dollar．But now，l can only buy two because the cost has (上涨)to 50 cents．In other words，the value of one dollar has dropped over the years．''
Daniel nodded his head．Now he was a little (确信)what his uncle meant．Bob smiled．
