A stock priced at $100 has a 70 percent pr
题型：单项选择题
问题：
A stock priced at $100 has a 70 percent probability of moving up and a 30 percent probability of moving down. If it moves up, it increases by a factor of 1.02. If it moves down, it decreases by a factor of 1/1.02. What is the probability that the stock will be $100 after two successive periods（）
A. 9%.
B. 42%.
C. 21%.
