Aresearcher collects a simple random sample of grade-point averages of statistics students, and she calculates the mean of this sample. under what conditions can that sample mean be treated as a value from a population having a normal distribution? select all that apply. a. the researcher collects more than 30 samples. b. the sample has more than 30 grade-point averages. c. if the population of statistics students has a normal distribution. d. if the population of grade-point averages has a normal distribution.