A sample of 25 seniors from a large urban school district has a mean Verbal SAT score of 450. Assume we know that the standard deviation of the population of Verbal SAT scores for seniors in the district is s=100. A 90% confidence interval for the mean score µ for the population of seniors is used. Which of the following will produce a confidence interval with a smaller margin of error?

Using a confidence interval of 95%
Using a sample of 100
Using an upper critical value of 99%
Using a sample of 15 seniors
Using any sample size smaller than 25