1.A number of factors are accountable for this situation. 　　A number of factors might contribute to (lead to )(account for ) the phenomenon(problem). 　　2. The answer to this problem involves many factors. 　　3. The phenomenon mainly stems from the fact that... 　　4. The factors that contribute to this situation include... 　　5. The change in ...largely results from the fact that... 　　6. We may blame ...,but the real causes are... 　　7. Part of the explanations for it is that ... 　　8.One of the most common factors (causes ) is that ... 　　9.Another contributing factor (cause ) is ... 　　10.Perhaps the primary factor is that … 　　11.But the fundamental cause is that ... 　　12.The reason why + 句子 is that + 句子 (...的原因是...) 　　13.This phenomenon exists for a number of reasons .First,…….Second,…….Third，……。這一現(xiàn)象存在有很多原因的，第一……第二……第三…… 　　14.For one thing,…… For another thing，…… ==On the one hand,……On the other hand……一方面……另一方面…… 　　15.I quite agree with the statement that……The reasons are chiefly as follows.我十分贊同這一論述，即……。其主要原因如下。