There are three reasons for this.
The reason for this are as follows.
The reason for this is abvious.
The reason for this is not far to seek.
The reason for this is that.
We have good reason to believe that.
There are three reasons for the changes that have taken place in our life.
(Great change has taken place in our life, there are three reasons for this.)
Firstly，people’s 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．