单项选择题Put 8 identical balls into 3 different boxes, each box has at least 2 balls.How many different ways to put the balls? ( )(A)6(B)12(C)18(D)36(英汉词典:identical完全相同的)
单项选择题路面位于岩石或填石路基路段时,应在石方顶面应铺设( ),厚度200mm~300mm。 A. 整平层 B. 垫层 C. 透层