美式看跌期权( )执行。
A．可以在未来的任何时刻
B．只能在分派红利后
C．只能在到期日
D．可以在到期日或之前的任何一天
参考答案：D
设集合A={-3，a+1，a2}，B={2a-1，a-3，a2+1}，若A∩B={-3}，试求a与A∪B．
. John hadn’t been able to quit smoking at once; he had to control his smoking desire .
A．more or less
B．by and by
C．little by little
D．now and then
