问题
单项选择题
Which of the following qualifies as a cumulative distribution function（）
A. F(1)=0.5, Y(2)=0.25, F(3)=0.25.
B. F(1)=0, F(2)=0.5, F(3)=0.5, F(4)=0.
C. g(1)=0, F(2)=0.25, F(3)=0.50, F(4) =1.
答案
参考答案：C
解析：
Because a cumulative probability function defines the probability that a random variable takes a value equal to or less than a given number, for successively larger numbers, the cumulative probability values must stay the same or increase.