If two independent samples are used in a hypothesis test concerning the difference between population means for which the combined degrees of freedom is 25, which of the following is true about the sample sizes, n1 and n2?
a) n1 = 13 and n2 =14
b) cannot be determined from the given information
c) n1 = 15 and n 2 =12
d) n1=12 and n2 = 13