THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION

THE NEXT QUESTIONS ARE BASED ON THE FOLLOWING INFORMATION:
Independent samples of math scores from students in the U.S.and Europe were collected from normal populations.A sample of 50 students from the U.S.had an average score of 570 while a sample of 50 European students had an average score of 540.The population standard deviations for the average scores of the US and European students are 102 and 115 respectively.
-The confidence interval for the difference between two population means that are normally distributed where the population variances are unknown and are not assumed to be equal rely on the use of:

A) the average sample variance.
B) the estimated sample variance.
C) Satterthwaite's approximation.
D) the pooled variance.