原因

number of factors are accountable for this

A number of factors might contribute to (lead to )(account for ) the phenomenon(problem).

The answer to this problem involves many

The phenomenon mainly stems from the fact

The factors that contribute to this situation

The change in results from the fact

We may blame ,but the real causes

Part of the explanations for it is that

One of the most common factors (causes ) is that

Another contributing factor (cause ) is

Perhaps the primary factor is that …

But the fundamental cause is that