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...
1.It has the following advantages.
2.It does us a lot
3.It benefits us quite a lot.
4.It is of great benefit to us.
1.It has more disadvantages than advantages.
2.It does us much harm.
3.It is harmful to us.
1.It is important(necessary，difficult，convenient，possible)for sb.to do sth.
2.We think it necessary to do sth.
3.It plays an important role in our life.
1.We should take some effective measures.
2.We should try our best to overcome(conquer)the difficulties.
3.We should do our utmost in doing sth.
4.We should solve the problems that we are confronted(faced)with.
1.Some changes have
taken place in the past five years.
2.A great changewill certainly be produced in the world’s communications.
3.The computer has brought about many changes in education.