In the passage, the author argues that we should be cautious of any claims that state that parents have a"biologically delimited, once-in-a-lifetime opportunity to help their children build better brains". This is so because neuroscientists have found that the brain is capable of readjusting after a new experience or trauma, and also that "the brain is far from set in its trajectory even at the completion of adolescence". Lines "Some might ask.... a good argument" questions the above claims and precedes an opposing idea. Thus we can deduce that C is the best answer. The other options are incorrect as they do not fit the context.