下面哪项不是超声波的特性（）
A.束射性
B.反射
C.不同组织传播速度一致性
D.散射
E.折射
参考答案：C
(2012·福建高考)China recently tightened its waters controls near the Huangyan Island to prevent Chinese fishing boats from ________ in the South China Sea.
A．attacking
B．having attacked
C．being attacked
D．having been attacked
只能在期权到期日执行的期权属于（）。
A．看跌期权
B．欧式期权
C．看涨期权
D．美式期权
