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.
以下这些是造成这一问题的最主要/最好/最重要/最大/最有意义/明显/至关重要的原因。
This is based on the propensity(倾向，原因) of following points.
这基于以下的原因。
The main reason is that.. 主要原因是_____________。
One very important argument for ..... is that....
_______的非常重要的原因便是____________________。
The reasons are quite clear. Above all, ....
原因非常清楚。首先(首要的是)__________。
The first reason can be seen by every person.
第一个原因其实很明显。
The first and most important reason is that.....
第一个而且最重要的原因是______________。
One of the reasons that are given for....is that....
______________的原因之一是__________________。
Perhaps this is because of the simple fact that.....
也许，原因很简单，亦即_____________________。
One of the premier causes is that(注意用词)
最重要的原因之一便是______________。