单项选择题
A.0.1 B.0.3 C.0.5 D.0.7
A.孔深<1.8 B.1.8≤孔深<2.5 C.2.5≤孔深<5.0 D.孔深≥5.0
A.4%~6% B.5%~7% C.6%~8% D.7%~9%