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...
比如：
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把握，可将它改写成两个句子。如：Great changes have taken place in our life. There are three reasons for this.如此写可以防止套用中的表达失误。
2.表示好处
1)It has the following advantages.
2)It does us a lot of good.
3)It benefits us quite a lot.
4)It is beneficial to us.
5)It is of great benefit to us.
比如：
Books are like friends.They can help us know the world better，and they can open our minds and widen our horizons.Therefore，reading extensively is of great benefit to us.
3.表示坏处
1)It has more disadvantages than advantages.
2)It does us much harm.
3)It is harmful to us.
比如：
However，everything divides into two.Television can also be harmful to us.It can do harm to our health and make us lazy if we spend too much time watching television.
4.表示要紧、必要、困难、便捷、可能
1)It is importantfor sb.to do sth.
2)We think it necessary to do sth.
3)It plays an important role in our life.
比如：
Computers are now being used everywhere，whether in the government，in schools or in business.Soon， computers will be found in every home，too.We have good reason to say that computers are playing an increasingly important role in our life and we have stepped into the Computer Age.
5.表示手段
1)We should take some effective measures.
2)We should try our best to overcomethe difficulties.
3)We should do our utmost in doing sth.
4)We should solve the problems that we are confrontedwith.
比如：
The housing problem that we are confronted with is becoming more and more serious.Therefore，we must take some effective measures to solve it.
6.表示变化
1)Some changes have taken place in the past five years.
2)A great change will certainly be produced in the worlds communications.
3)The computer has brought about many changes in education.
比如：
Some changes have taken place in peoples diet in the past five years.The major reasons for these changes are not far to seek.Nowadays，more and more people are switching from grain to meat for protein，and from fruit and vegetable to milk for vitamins.
7.表示事实、近况
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.
比如：
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 pollutionThe government on its part should also design stricter laws to promote a cleaner environment.
