1.Some reasons eaIl explain this trend.First of all，…Secondly，…Furthermore，…一些原因可以解释这一趋势。首先，……其次，……另外，……

　　2.Perhaps the main/primary/fundamental/most important reason is…也许，最主要(根本)的原因是……

　　3.A number of factors could account for/contribute/lead to/resuh in the change of…Firstly，…Secondly，…Thirdlv.…引起……变化的原因有好多，首先，……其次，……再次，……

　　4.why…? For one thing，…for another，…为什么……?第一，……第二，……

　　5.There are many reasons explaining this case.As for me，I consider the following as the typical ones.To begin with, …Secondly，…Last but not least，…有很多原因可以解释该问题。就我而言，我认为以下原因比较典型。一个是……第二个是……最后，……

　　6.There are many reasons responsible for this instance，and the following are the typical ones.In the first place….In the second place，…导致这种现象的原因有好多，以下是其中比较有代表性的。第一个是……第二个是……

　　7.Any discussion about this problem would inevitably involve…任何对此问题的讨论都不可避免地涉及到……

　　8.Fmm my everyday experience and observation I can state several factors that defend the statement that…根据我的日常经验和观察，我可以举出几个因素来证明……

　　9.Certainlv.…is not the sole reason for…，…is also responsible for the change/problem.当然，……并不是唯一的原因。还有……也导致了这一变化(问题)的产生。

　　10.The causes for…are varied.They include…Perhaps the main cause is…造成……的原因有好多，包括……。主要的原因可能是……

　　11.There are probably three/many/several/a varieties of reasons/causes for this dramatic/significant increase/decline in…引起……显著增长(下降)的原因有三个(许多、几个、很多)

　　12.Among the most sound/convincing reasons given/identified/advanced by people for…，one should be mentioned/emphasized.在各种常为人们所道的理由中，应特别提一下……

　　13.Another reason why I disagree with the above statements is that I believe…我不同意上述观点的另一个原因是因为我相信……

　　14.Thanks to/Owing to/Due to/Becanse of/As a resuh of…因为……

　　15.It is no easy task to identify the reasons for this phenomenon which involves several complicated factors?要找出这一现象的原因并非易事，因为它涉及到若干复杂的因素。

　　16.We may blame/criticize…for…，but the causes/roots for the problem/phenomenon/trend go much deeper.我们或许会批评……因为……但是这一问题(现象、趋势)背后有着更深层次的原因。

　　17.The reason for this is not far to seek.The first reason is that…The second one is…The third is…For all this, the main cause of…is due to…这一问题的原因不难发现。第一个原因是……第二个是……第三……综上所述，……最主要的原因应该是……

　　18.One may attribute/ascribe/owe the increase/decrease/change to…人们可能将这一增长(下降、变化)归因于……

　　19.You don't have to look very far to find out/identify the reason why…你不必花费很大的力气就会找到……的原因。

　　20.The success/failure mainly stems/results/arises/comes from the fact that…这一成功(失败)主要源于这样一个事实……

　　21.There are numerous reasons why…，and 1 would explore only a few of the most important ones here.……的原因有很多，这里我只想探讨其中几个最重要的原因。