阅读下面短文，掌握其大意，然后从21~40各题所给的四个选项（A、B、C和D）中，选出最佳选项，并在答题纸上将选项标号涂黑。
Have you heard of the story of “spilt milk?” Well, we all know it is no use crying over spilt milk. But this story is 21 .
A famous scientist had 22 several very important medical discoveries. He was asked in an interview 23 set him so far apart from others.
He responded that it all came from an 24 with his mother that occurred when he was about two years old. He had been trying to 25 a bottle of milk from the refrigerator when he
26 hold of the slippery bottle and it fell, spilling its contents all over the kitchen floor --- 27 milk!
When his mother came, instead of yelling at him or giving him a 28 , she said, “You know, Robert,
