A.38,40,46,56,79,84 B.40,38,46,79,56,84 C.40,38,46,56,79,84 D.40,38,46,84,56,79
A.8 B.3 C.5 D.9
A.(rear-front+m)%m B.read-front+1 C.read-front-1 D.read-front