Which of the Following Is the Best Definition for the Concept

Which of the following is the best definition for the concept of normal distribution?

A) The excess return required from an investment in a risky asset over a risk-free investment.
B) Market in which security prices reflect available information.
C) A symmetric, bell-shaped frequency distribution that can be defined by its mean and standard deviation.
D) The average compound return earned per year over a multi-year period.
E) The hypothesis is that actual capital markets are efficient.