因为clever是双音节，有两个元音。音节是按元音分的，一个音节包含一个元音，比较级两种都可以。clever比较级两种形式：ducleverer、more clever，都表示更聪明的，较聪明。
clever例句
1、He's a very clever man
他非常聪明。
2、A colleague of mine in Milan devised the following very clever little experiment.
我在米兰的一个同事设计了下面这个非常巧妙的小实验。
3、His many admirers describe him as clever: his enemies as too clever by half.
崇拜他的人很多说他聪明；恨他的人则说他聪明过了头。
4、My sister was always a lot cleverer than I was
我妹妹向来比我聪明许多。
5、Her mother was clever at many things.
她妈妈对许多事情都很精通。