The df (degrees of freedom) for the F-ratio in a randomized ANOVA equals the number of groups minus one for the numerator (between-group variability) and the total number of participants minus the number of groups for the denominator (within-group variability).
In this case, there are four groups with 15 participants in each group, so the total number of participants is 4 x 15 = 60. Therefore, the denominator df is 60 - 4 = 56.
The numerator df is equal to the number of groups minus one, which is 4 - 1 = 3.
So the correct answer is option d) 3, 56.