阅读理解

阅读语言材料，然后按要求做题。

　　Little Tommy Was doing very badly in math．His parents had tried everything－tutors(家庭教师), cards, special learning centers－in short, everything they could think of．Finally they took Tommy to a catholic(天主教的)school．

　　After the first day, little Tommy came home with a very serious look on his face．He didn't kiss his mother hello．Instead, he went straight to his room and started studying．Books and papers were spread(铺开)out all over the room and little Tommy was hard at work．His mother was surprised．She called him down to dinner and as soon as he finished eating, he went back to his room、without a word．In no time he was back hitting the books as hard as before．This went on for some time．day after day while the mother tried to understand what was happening·

　　Finally, little Tommy brought home his report card．He quietly put it on the table and went up to his room and hit the books．His mom looked at it and to her surprise, little Tommy got all A in math．She could no longer hold her curiosity(好奇心)．She went to his room and asked, “Son, what was it? Was it the nuns(修女)?”

　　Little Tommy looked at her and shook his head, “No．''

　　‘’Well then, ”she asked again．‘’WHAT was it?”

　　Little Tommy looked at her and said, "Well, on the first day of school, when I saw that man nail(钉)to the plus sign(加号), I knew they weren't joking．”

根据材料内容选择最佳答案。