答案：C

考查主语从句。_______ Japan’s nuclear crisis (核危机) will be solved in 2011在主从复合句_______ Japan’s nuclear crisis (核危机) will be solved in 2011 is not known yet中作主语。根据is not known yet，还不知道，可知主语从句表不确定，应由Whether引导，If 不能引导主从。所以选C。