Many difficulties have --- as a result of the change over to

选C
raise是及物动词,此句若要用raise须这样改：Many difficulties have been raised as a result of ...
rise和arise都是不及物动词,但arise有出现／呈现的意思 而rise作动词时意思多与升起有关
找到一例句作参考：Difficulties arose out of the shortage of petroleum.困难起因于缺乏石油．