嗨，大家好！我们知道cloud有“云，云朵”的意思，nine是数字九，那be on cloud nine是什么意思呢？
be on cloud nine的意思是“to be extremely happy and excited”，即“异常兴奋，乐不可支，高兴极了”。这句习语最开始是指美国气象局在20世纪50年代定义的云的一种分类。据说，这种云通常指积雨云或雷雨。它常常高达四万英尺。当你在这样的云层上时，你简直是在世界之巅。所以后来这句习语就引申为“高兴极了”。
例句：
A:Was Mike pleased about getting that job?
B:Pleased?He was on cloud nine!
A：迈克得到那份工作高兴吗？
B：岂止是高兴？他简直飘飘然了！
下面再介绍两个有用的习语：
be on familiar terms
be on familiar terms的意思是“to have a close and informal relationship”，即“关系亲密”。
例句如下：
They had met before, but they were hardly on familiar terms.
他们以前见过面，但并不是很熟。
be on another planet
be on another planet的意思是“to not give attention to what is happening around you and to think differently from other people”，即“像是生活在另一个星球，怪异”。
举个例子：
Some days that boy seems as if he's on another planet.
那个男孩有时候看来很怪异。
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