The following factors/reasons/cause need to be taken into consideration.
There are several reasons contributing to…/accounting for…
The reasons for…are varied. For one thing…for another…
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.
为什么___________，原因很多，在此列举几个较为重要的原因。
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。
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______________。
We may look into every possible reason, however, foremost reason for .... Is ....
其实有很多原因，不过，造成________的最重要的原因是______________。
