A state study on labor reported that one-third of full-time teachers in the state also worked part time at another job. For those teachers, the average number of hours worked per week at the part-time job was 13. After an increase in state teacher salaries, a random sample of 400 teachers who worked part time at another job was selected. The average number of hours worked per week at the part-time job for the teachers in the sample was 12.5 with standard deviation 6.5 hours. Is there convincing statistical evidence. at the level of a = 0.05, that the average number of hours worked per week at part-time jobs decreased after the salary increase? 
选项为:A:No. The p-value of the appropriate test is greater than 0.05.  B:No. The p-value of the appropriate test is less than 0.05.  C:Yes. The p-value of the appropriate test is greater than 0.05.  D:Yes. The p-value of the appropriate test is less than 0.05.  E:Not enough information is given to determine whether there is convincing statistical evidence.  请回答其中一个选项.