级配碎石
参考答案：
粗、中、小碎石集料和石屑各占一定比例的混合料，当其颗粒组成符合规定的密级配要求时，称做级配碎石。
简述瀑布基本结构组成。
Good anchorage may be obtained anywany, generally mud and sand, in this water area. Vessel may have（）.
A.good towing ground
B.good holding ground
C.good grabbing ground
D.good dragging ground
