in my mind , the following factors/reasons/causes need to be taken into consideration.
我认为，我们需要考虑下列因素/原因：
There are several reasons for this phenomenon/why...-(as follows).
造成这种现象的原因如下：
And I would like to present two explanations for this:
对于此，我有如下两点愚见：
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。
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______________。
At the risk of sounding too simplistic, it seems to me that the main propositions can be summarized in one saying.
这个原因可能较简单，不过，我认为可以用一句谚语来概括，________。
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______________。
It might also be noted that....
需要注意的是，____________。
Another reason why .....(凑字数，但不可滥用) is that....(有利于写长句)
What is also worth noticing is that....
值得一提的是___________________。