问题
单项选择题
If a smooth curve is to represent a probability density function, what two requirements must be satisfied The :（）
A. area under the curve must be zero and the curve must not fall below the horizontal axis.
B. area under the curve must be one and the curve must not rise above the horizontal axis.
C. total area under the curve must be one and the curve must not fall below the horizontal axis.
答案
参考答案：C
解析：
If a smooth curve is to represent a probability density function, the total area under the curve must be one ( probability of all outcomes equals 1 ) and the curve must not fall below the horizontal axis (no outcome can have a negative chance of occurring).