单项选择题
A.220 B.280 C.350 D.400
A.上柱:l0=4.1,下柱l0=6.8 B.上柱:l0=4.1,下柱l0=10.6 C.上柱:l0=5.0,下柱l0=8.45 D.上柱:l0=6.6,下柱l0=8.45