A researcher is estimating the average commute time in a city. With a sample of 100 commuters, the 95% confidence interval for the mean is $[25,35][25,\; 35]$[25,35]. What will happen if they increase the sample size to 400 commuters?

1. A) The interval will become narrower.
2. B) The interval will become wider.
3. C) The interval will remain the same.
4. D) The interval will shift upward.