Which of the following sample results yields a 95% CI for with the smallest width and

Which of the following sample results yields a 95% CI for μ with the smallest width and why?

(i) x = 28, s = 5, n = 61

(ii) x = 32, s = 4, n = 30

(iii) x = 25, s = 3, n = 20

(iv) x = 40, s = 6, n = 121.

As an experiment, 10,000 people are completely genotyped, of whom 10 have the (aa) genotype, 630 have the (aA) genotype [i.e., either (aA) or (Aa)], and 9360 have the (AA) genotype.