Perhaps this is because of the simple fact that…..

　　也許，原因很簡單，亦即_____________________。

　　One of the premier causes is that(注意用詞)

　　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.

　　這個原因可能較簡單，不過，我認為可以用一句諺語來概括，________。

　　We may look into every possible reason, however, foremost reason for …. Is ….

　　其實有很多原因，不過，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 …..(湊字數，但不可濫用) is that….(有利于寫長句)

　　What is also worth noticing is that….

　　值得一提的是___________________。

　　There is another factor that deserves some words here.

　　還有另外一個很重要的原因。

　　A more essential factor why…. Is that

　　________ 的更為重要的原因是____________。

　　A further reason why,,,, is that…..

　　________的更深層次的原因是____________。

　　In addition..此外，再者

　　Moving on to wider themes,_______

　　展開來說，_________________________。

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

　　第二個原因也很重要(值得考慮)，亦即__________。

　　Likewise(同樣), common sense tells us that…

　　同樣，___________，這是眾所周知的。

　　The third but very important reason is that…