A.R≈0.07ρ B.R≈0.05ρ C.R≈0.28ρ D.R≈0.04ρ
A.R≤250/I B.R≤2000/I C.R≤12 D.R≤10
A.0.8,1.2 B.0.8,1.8 C.0.6,1.2 D.0.6,1.8