题目

    There was a boy who was sent by his parents to a boarding school (寄宿学校).  36  being sent away, this boy was the 37 student in his class. He was at the top in every  38  always with high marks.     But the boy changed after  39 home and attending the boarding school. His grades started  40 .  He hated being in a  41.  He was lonely all the time. And there were especially dark times when he 42  committing suicide (自杀). All of this was because he felt  43  and no one loved him.     His parents started  44  about the boy. But they even did not know 分子式为C5H10O的醛应有（　　）A．2种B．3种C．4种D．5种