1. Now that we know that...

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

　　3. The change in... largely results from the fact that...

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

　　5. A number of factors could account for the development in...

　　6. Perhaps the primary reason is...

　　7. It is chiefly responsible for...

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

　　9. There are several possible reasons， except that...

　　10. Somebody believes/ argues/ holds/ insists/ thinks that...

　　11. It is not simple to give the reason for this complicated phenomenon...

　　12. Different people observes it in different ways.

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