Aresearcher is planning to construct a one-sample z? confidence interval for a population mean ? . select the statements that would lead to a smaller margin of error, assuming the other factors remain the same.

a) the population standard deviation turns out to be higher than expected.

b) the researcher increases the sample size.

c) the researcher lowers the confidence level.

d) the researcher decreases the sample size.

e) the population standard deviation turns out to be lower than expected.

f) the researcher raises the confidence level.