单项选择题
A.its velocity in knots B.direction from which it flows C.estimated current D.direction toward which it flows
A.interruption of the normal current flow by the footing B.elevating in mud-slide zones C.penetrating rapidly through a hard crust into weaker soils D.extracting legs from soils with high cohesion
A.pick up speed where the channel widens B.run slower in the center of the channel C.hug the inside of a bend D.cause the greatest depth of water to be along the outside of a bend