应该选C.
in case万一.是连词,引导条件状语从句.也就是说in case后面是一个完整的句子.比如：Take a hat with you in case the sun is very hot. 倘若太阳很利害,你就把帽子戴上. in case of的of是介词,介词后面只能带名词性质的词,比如名词、代词等.意思和in case差不多,万一的意思.比如： In case of rain they can't go. 万一下雨,他们就不能去了. in the case of,就...来说, 关于.意思跟上面两个不一样了.一般表示转而提及另一件事情.比如：In the case of woman,they have more difficulty in their job.就女性来说,她们在工作中会遇到更多的困难.