简析下面这段对话的言外之意。     

        孔融10岁时，前去拜望名士李元礼。闲谈之中，众人都夸赞孔融奇才早慧， 唯独一个姓陈的不以为然地说：“小时候机灵，长大了未必就聪明。”孔融听后立即说道：“想你陈先生小时候一定很机灵。”请问：孔融的言外之意是什么？

---John, how did your English exam go?

-----I thought I ____,but in fact I came in the top 10% in the class.

A．should have failed

B．couldn’t have failed

C．might have failed

D．mustn’t have failed