Why Is a Post-Hoc Test Necessary If You've Used a One-Way

Multiple Choice

Why is a post-hoc test necessary if you've used a one-way ANOVA to avoid the problem of multiple comparisons?

A) Accounting for their respective standard deviations increased the alpha level.
B) In the case of a significant F value, you were unsure of how the three groups differed.
C) It was necessary to set a new error rate for each individual t-test.
D) All these are correct.