A.由下而上分層開挖 B.由左而右分層開挖 C.由而上分下層開挖 D.逐步掘進(jìn)開挖
A. 1:0.3 B. 1:0.5 C. 1:0.7 D. 0.3:1
A.300m B.250m C.200m D.150m