A.3.7,4.2B.4.0,3.5C.4.2,3.7D.5.0,4.5
A.5,≦0.2B.10,≦0.3C.15,≦0.2D.20,≦0.3
A.3-2-1原则B.6-2-1原则C.N-2-1原则D.5原则