In the selection of volunteers in a city, the known situation is as follows: (1) only Xiao Hong signs up, Xiao Bai, Xiao Hei and Xiao Hua will all sign up; (2) if Xiao Bai does not register, Xiao Hei will not register; (3) if Xiao Hei does not register, then Xiao Hui does not register; (4) Xiao Hong did not sign up; (5) Xiao Hui signed up
Both Xiao Bai and Xiao Hei have signed up