Final answer:
The largest critical value is t20,0.025.
Step-by-step explanation:
To determine which of the given critical values is the largest, we need to compare the values for t-distribution and z-distribution. The t-distribution critical values, t10.0.025 and t20,0.025, represent the values for confidence level 95% and sample sizes 10 and 20 respectively. The z-distribution critical values, Z0.025 and Z0.05, represent the values for confidence level 95% and 99% respectively.
Since we know that the t-distribution has thicker tails compared to the z-distribution, the larger critical values will be for the t-distribution. Therefore, the largest critical value is t20,0.025 (option b).