单项选择题
A.反弯曲线 B.C型曲线 C.断背曲线 D.S型曲线
A.-1.5%或-2% B.-2.5%或-3% C.-3.5%或-4% D.-4.5%或-5%
A.20000m B.10000m C.5000m D.15000m