The normal probability curve:

a. makes it simple to work out the distribution of the mean of a random variable with a small number of observations (say more than 20 or 30).

b. describes a random variable that is less likely to lie within two standard deviations from the mean than outside two standard deviations from the mean.

c. lies in the range of 0 to 1.

d. is strongly negatively skewed.

Choose the most right option and explain why.