The number of sit-ups that all tenth-grade girls can do in 5 minutes is normally distributed. Beth surveyed 20 of her fellow intramural tennis players, all tenth-grade girls, and determined the mean number of sit-ups they could do. Can she make an inference about the population mean for all tenth-grade girls based on the sample? No, because the sample size was not big enough. No, because she did not use a simple random sample. Yes, because the sample size was big enough. Yes, because she used a simple random sample.