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___________________.

　　There is another factor that deserves some words here.

　　还有另外一个很重要的原因。

　　A more essential factor why… Is that

　　________ 的更为重要的原因是____________.

　　A further reason why,,,, is that……

　　________的更深层次的原因是____________.

　　In addition此外，再者

　　Moving on to wider themes,_______

　　展开来说，_________________________.

　　The second thing that must be taken into consideration is that…

　　第二个原因也很重要（值得考虑），亦即__________.

　　Likewise（同样）， common sense tells us that…

　　同样，___________,这是众所周知的。

　　The third but very important reason is that…