\textbf{High school students from track teams in the state participated in a training program to improve running times. Before the training, the mean running time for the students to run a mile was 402 seconds with standard deviation 40 seconds. After completing the program, the mean running time for the students to run a mile was 368 seconds with standard deviation 30 seconds. Let X represent the running time of a randomly selected student before training, and let Y represent the running time of the same student after training. Which of the following is true about the distribution of X - Y ?} 
选项为:A:\textbf{The variables X and Y are independent; therefore, the mean is 34 seconds and the standard deviation is 10 seconds.}  B:\textbf{~The variables X and Y are independent; therefore, the mean is 34 seconds and the standard deviation is 50 seconds.}  C:\textbf{The variables X and Y are not independent; therefore, the standard deviation is 50 seconds and the mean cannot be determined with the information given.}  D:\textbf{The variables X and Y are not independent; therefore, the mean is 34 seconds and the standard deviation cannot be determined with the information given.}  E:\textbf{The variables X and Y are not independent; therefore, neither the mean nor the standard deviation can be determined with the information given.}  请回答其中一个选项.