A.3~1km B.10~3km C.15~5km D.50~20km
A.0.02s B.0.05s C.0.1~0.25s D.0.25~0.5s
A.δu=u1-△u1 B.δu=δu1+e-∑△u C.δu=δu1+e-∑△u D.δu=δu1+e-(δu11+△uT+δu12)