再来一道低级的ps，求过程

norlanzhang

The residents of town x participated in a survey to determine the number of hours per week each resident spent watching television. The distribution of the results of the survey had a mean of 21 hours and a standard deviation of 6 hours. The number of hours that Pat, a resident of town x, watch television last week was between 1 and 2 standard deviation below the mean.Which of the following could be the number of hours that Pat watch television last week?
(A) 30
(B) 20
(C) 18
(D) 12
(E)  6

quick430

p看电视时间21-6到21-12之间，就是低于平均值的一个标准差和两个标准差之间，9到15，选12那个

xiaxiaqin

你这是神马考古什神马考古啊！！！