Answer:
D. The distance from the mean to an inflection point
Explanation:
We rarely encounter the actual formula for the normal PDF. It is ...
![p(x)=(1)/(√(2\pi))e^{-(x^2)/(2)}](https://img.qammunity.org/2021/formulas/mathematics/college/vhn1ruadqrenx6es19i3aemsk0si8cf0uu.png)
In fact, the inflection points are at x = ±1, where the curve changes from being concave downward to concave upward.
So, one standard deviation is the distance from the mean to an inflection point.