Four research teams each used a different method to collect data on how fast a new iron skillet rusts. assume that they all agree on the sample size and the sample mean (in days). use the (confidence level; confidence interval) pairs below to select the team that has the smallest sample standard deviation.

a. confidence level: 99.7%; confidence interval: 40 to 40
b. confidence level: 95%; confidence interval: 40 to 50
c. confidence level: 68%; confidence interval: 43 to 47
d. confidence level: 95%; confidence interval: 42 to 48