【单选题】

C

   John  Hewitt   studies  the   biology  of   itell  igence.  He’s  also  a  parent .Over  the  years. Hewitt  has   drawn  on  his   scientific  knowledge   in  making  parenting  decisions.
   I’m  a  father   of  four   children  myself.I  never  worried   too  much  about  the   environments  that  I  was   providing  for   my  children , because  I   thought  it   would  all  work   out  in  the  end   anyway  heng-aren’t  the  genes  especially  powerful?”  Hewitt  says.   He  knew   intell  igence  has  a   strong   biological  part.  If  your   parents   are   smart  You’ll  probably  be  smart.
But  recently . Hewitt  discovered   something  that   surprised  him.”well,I may  have  been   wrong,”he  amdits .It  is  the   environmental  increase  you  can  get. Or  the  harm  you  can  suffer  though  hard  times  that  may  be  a  little  more  important  in   adolescence(青春期）than   I  had  thought.
Howitt  and  other    was  an  extened   sensitive  period   in   the  higher  IQ inpiduals   or   another   way   of  looking   at  it  is  that   the  sensitivity to  the  environment   which  is  characteristic  of   earlier   childhood  seems  to  end   earlier  for  in  piduals   with  a  lower  IQ ,Hewitt  says  smart  kids  may  tend  to  take  part in  challenging  activities  and  this  keeps  them  ready  to   consider  learning  or  it   could  be  that   lead  to a  high  IQ  also cause  an  extended  leaming  period.
An  extended  learning  period   does   not   neccssarily  mean a   further  increase  in  the  IQ  .But  a  very  smart   teenager   with  an  extended  “sensitive  period” of  learning  might  be  able  to  pick  up   a  new   language  or  a   musical  instrument.  Such   learning  can  have  long  term  benefits.
“even  if  in  the   end   IQ   ends  up  being  determined   to  a   large  extent  by  the   genes  ,if  there’s  bee  aperiod  where  the  environment  makes a  difference   ,that  could  have  lifelong  consequences ,”Hewitt says.
.Hewitt originally  though  the   most   important  thing  affecting  kid’s  intellingence  was       .
A. the  gene  B.the environment  C.the  parenting decision D.the  scientific knowledge