Why have some tribes joined the Iraqi police and army?
A.
They hate of being Sunni rebels in Ramadi.
B.
They want to drive al-Qaida members from their region.
C.
They would be able to move to southern city of Diwaniyah with military force.
D.
They intend to stop rising influence of Shiite militia loyal to Moqtada al-Sadr.