1、It can be said with certainty that...可以肯定地说......
2、What calls for special attention is that...需要特别注意的是
3、It's generally recognized that...它普遍认为...
4、But the problem is not so simple. Therefore然而问题并非如此简单，所以……
5、Nothing is more important than the fact that...没有什么比这更重要的是…