article: There was a little boy with a bad temper .His father gave him some nails to drive into the fence  when he lost his temper .The first day the boy drove 37 nails into the fence .Then it began to become less . He found it was easier to hold his temper than to drive those nails into the fence .
  Finally the day came when the boy didn't lose his temper at all . He told his father about it and the father suggested that the boy should now pull out one nail for each day that he  held his temper .The days passed and the young boy was finally able to tell his father that all the nails were gone .
  The father took his son by the hand and led him to the fence .He said , "You have done well ,my son ,but you look at the fence . It will never be the same .When you say things in anger ,they leave a scar just like this one .You can put a knife in a man and draw it out . It won't matter how many times you say I'm sorry ,the wound  is still there .A verbal  wound is as bad as a physical one.
question: The word "it" in "it began to become less"refers to     _   .
options: the first day the fence the nails the boy's temper