某堤防为透水地基,渗透系数k 0 =6.7×10 -5 m/s,设计水头H=5m,堤顶宽度B=8m,上游坡坡率m 1 =4.0,下游坡坡率m 2 =5.0,透水地基厚T=30m,渗流量q 2 =1.2×10 -4 m 3 /(s·m),堤身渗流量q 1 =6.7×10 -5 m 3 /(s·m),出逸点高度h 0 =1.22m,背水侧无水。堤防下游沿渗出段y=0.2m及地基段x=0.4m的出逸比降分别为( )。 A.J y =0.20,J x =O.22 B.J y =0.20,J x =0.39 C.J y =0.31,J x =0.39 D.J y =0.31,J x =0.22