多大的数字被称为天文数字（）
A.千万以上
B.亿以上
C.千亿以上
参考答案：B
A stock priced at $ 20 has an 80 percent probability of moving up and a 20 percent probability of moving down. If it moves up, it increases by a factor of 1.05. If it moves down, it decreases by a factor of 1/1.05. What is the expected stock price after two successive periods（）
A. $ 20.05.
B. $ 22.05.
C. $ 21.24.
下列哪项不是阿托品的药理作用（）
A.中枢兴奋作用
B.松弛内脏平滑肌
C.促进腺体分泌
D.升高眼内压，调节麻痹
E.扩张血管，改善微循环
