is not是不是；没有；不是；可不是；并不算；
例如It is not often that you get such an opportunity.
The problem is not primarily a financial one.
这个问题基本上不是财政问题。
The success of the system is not in doubt.
这种制度的成功确定无疑。
The company\'s financial position is not certain.
这家公司的财务状况不明朗。
