1)There are three reasons for this.
2)The reasons for this are as follows.
3)The reason for this is obvious.
4)The reason for this is not far to seek.
5)The reason for this is that...
6)We have good reason to believe that...
例：There are three reasons for the changes that have taken place in our life. Firstly, peoples living standard has been greatly improved. Secondly, most people are well paid, and they can afford what they need or like. Last but not least, more and more people prefer to enjoy modern life.
注：如考生写第一个句子没有把握，可将其改写成两个句子。如：Great changes have taken place in our life. There are three reasons for this. 这样写可以避免套用中的表达失误。
1)We cannot ignore the fact that...
2)No one can deny the fact that...
3)There is no denying the fact that...
4)This is a phenomenon that many people are interested in.
5)However, thats not the case.
例：We cannot ignore the fact that industrialization brings with it the problems of pollution. To solve these problems，we can start by educating the public about the hazards of pollution. The government on its part should also design stricter laws to promote a cleaner environment.