1. Among the most convincing reasons given，one should be mentioned…

2. The change in …largely results from the fact that

3. There are several causes for this significant growth in…，first …，second …，finally…

4. A number of factors could account for the development in…

5. Perhaps the primary reason is…

6. It is chiefly responsible of…

7. The reasons for…are complicated，And probably they are found in the fact…