Which of the following description of the role of the BBU slot is correct? (Multiple choice)
A . SLOT 2, 3 can be used to install the baseband board
B . SLOT 16, used to install the fan module FAN
C . SLOT 19 ， used to install the power module UPEU
D . SLOT 5, 6, 7 can be used to install the main control board
Answer: ABC