The test statistic for a related-samples t test is +2.100. Using a .05 level of significance, would you retain or reject the null hypothesis under each of the following conditions?

1. df = 10, two-tailed test 2. df = 30, one-tailed test (upper-tail critical)

3. df = 20, two-tailed test 4. df = 40, one-tailed test (lower-tail critical)