A.10%~20% B.20%~50% C.50%~70% D.70%~100%
A.下游調(diào)查河段長(zhǎng)度的1/4 B.下游調(diào)查河段長(zhǎng)度的1/2 C.下游調(diào)查河段長(zhǎng)度的3/4 D.與下游調(diào)查河段長(zhǎng)度相等
A.春季和夏季 B.秋季和冬季 C.春季和冬季 D.至少春季和秋季