A researcher wants to estimate the average life expectancy for Wisconsinites. She takes a random sample of 50 Wisconsinites and finds that the average life expectancy is 76.7 years. Also, she assumes that the population standard deviation is 4.5 years.

(b) To construct a 95% confidence interval for the mean life expectancy of all Wisconsinites, which one of the following z-scores should the researcher use?