{{*HTML*}}某砂土试样高度H=30cm，初始孔隙比e₀=0.803，比重G _s =2.71，进行渗透试验(见图)。渗透水力梯度达到流土的临界水力梯度时，总水头差Δh应为下列哪个选项? （）
                       

A．0.20s
B．0.35s
C．0.45s
D．0.55s

A．{{*HTML*}}d_u =7.0m；d_w =6.0m
B．{{*HTML*}}d_w =7.5m；d_w =3.5m
C．{{*HTML*}}d_u =9.0m；d_w =5.0m
D．{{*HTML*}}d_u =3.0m；d_w =7.5m