[求助]OG11--23

求教高手们一个问题，OG11中的第23题，maybe是情态动词，最后的答案当中怎么能没有他呢？答案解析中说probably可换，怎么回事啊？谢谢。

23. Of all the possible disasters that threaten American agriculture,the possibility of an adverse change in climate is

      maybe the more difficult for analysis.

      (A)is maybe the more difficult for analysis

      (B)is probably the most difficult to analyze

      (C)is maybe the most difficult for analysis

      (D)is probably the more difficult to analyze

      (E)is,it may be,the analysis that is most difficult

maybe不等于may be，是副词，不是情态动词

maybe主要用在口语中，而且放在句首；

非常感谢，我想了很久了。