如图所示，两根相距为l的平行直导轨ab、cd、b、d间连有一固定电阻R，导轨电阻

     Who is setting your standards (标准) for you?
      A true story has it that Mr. Miller, who was 70 years old, decided to    1    around the local high school
football field. As he ran along, a group of football players were in    2   .
     The players soon started sprinting (速跑) up and down the    3  . Mr.Miller told himself, "I'll just keep
running until they    4   ." So he ran. And they ran. He ran some more. And they    5    running too. He
kept running until he could finally run no more. Mr.Miller stopped. One of the     6    , equally tired, came up
to him and said, "Well, I'm glad you    7   stopped. Our coach (教练) told us we had to keep running    8   
you were running!"
     Mr.Miller was watching them and they were    9   him, too. He was letting them   10   his standards.
And the same time they   11   him to set theirs.
     After telling the story, some questions occur in my mind:Are you keeping   12   with somebody else?
Are you allowing other people to set your standards   13   you? Do you keep pace with those around you,
or do you   14   yourself just how you will   15   your life? You should know that it is you who must be 
 16   to determine what your standards will be. Set your standards too   17  , and you'll feel bored. Set
high standards   18   you can llive a   19    life. For only when you reach for the best that is within yourself,
will you   20  a wonderful life.