For a standard normal distribution, which of the following variables always equals 0?

In a standard normal distribution, the mean will always be equal to 0. 

Furthermore, the definition of a standard normal distribution is a normal distribution in which the mean is 0 and the standard deviation is equal to 1. Take note that standard normal distribution is a type of normal distribution and not all normal distributions have the same mean and standard deviation.

Ithink the answer is b