The says that, as we take more and more observations at random from any population, the distribution of the mean of these observations eventually gets close to a normal distribution.

 The correct answer is : The central limit theorem

Explanation:  This is a fundamental theorem of probability and statistics. When the sample size is large enough, the distribution of the means follows approximately a normal distribution. The theorem can be applied regardless of the form of population distribution.

i would say b. research typically uses a variety of sources

answer; through play and social interaction;