11. 某粒料篩分析中,各號篩上之粒料停留重量如下:#4-60g;#8-120g;#16-160g;#30-200g;#50-280g;#100-150g;底盤-30g,則其細度模數(F.M)為何?(A)2.31(B)2.51(C)2.71(D)2.91。