在天然水体中，常用( )来描述河流的混合特性。
A．径流模数
B．径流系数
C．横向混合系数
D．纵向离散系数
参考答案：C,D
"How could you lose so much money?" Charlie asked his wife, eyeing her angrily from _____ the kitchen table. [ ]
A. at
B. across
C. through
D. on
形成降水的充分和必要条件是什么？
