请问A为什么不对

问题如下：

Question Which of the following is best described as a discrete random variable?

选项：

A.The expected percentage change in a country’s gross national product for the next year B.The number of days on which the DJIA experienced an increase since 2013 C.The expected annual return on the Nikkei 225 Index over the next year

解释：

Solution

B is correct. A discrete random variable is a random variable that can take on at most a countable number of possible values. The number of days on which the DJIA experienced an increase since 2013 is the only choice with a discrete number of possible values.

A is incorrect. A percentage change is an example of a continuous random variable.

C is incorrect. A return is an example of a continuous random variable.