And I would like to present two explanations for this:
The reasons are chiefly as follows. 主要原因如下：
There are numerous reasons why ____, and I would like to explore a few of the most important ones here.
The reasons are presented below. 原因如下。
There are three premier(主要的)/best/ most important, largest, significant, obvious, crucial causes as follows.
This is based on the propensity(倾向，原因) of following points.
The main reason is that.. 主要原因是_____________。
One very important argument for ..... is that....
The reasons are quite clear. Above all, ....
The first reason can be seen by every person.