1. Everybody knows that...
2. It can be easily proved that...
3. It is true that...
4. No one can deny that...
5. One thing which is equally important to the above mentioned is...
6. The chief reason is that...
7. We must recognize that...
8. There is no doubt that...
9. I am of the opinion that...
10. This can be expressed as follows:
11. To take..， for an example ....
12. We have reason to believe that...
