The dot plot shows the results of two random samples measuring the mean time, in hours, spent working out in a given week. Which statement is true?

a
The slight difference in the distributions indicates that the training did not significantly change the students' race times.
b
The mean time the students took to finish the 30 free-throws decreased by about 3 seconds after training.
c
The mean time the students took to finish the 30 free-throws increased by about 3 seconds after training.
d
The significant difference in the distributions indicates that the training did not significantly change the students' race times.