more than 后面接一个数词的时候可以转化成over,如：
There are more than 30 students in the class.
=There are over 30 students in the class.
但是,如果more than 之后接其他成分,则不可以用over替换,如：
He is more than selfish. = He is very selfish. 他非常自私.
这时候就不能用over替换了