prep求助

ken178

A certain list of 100 data has an average (arithmetic mean) of 6 and a standard deviation of d, where d is positive.Which of the following pairs of data, when added to the list, must result in a list of 102 data with standard deviation less than d ?


(A) -6and 0

(B) 0 and 0
(C) 0 and 6
(D) 0 and 12
(E) 6 and 6

这题怎么解啊，标准差的题不会啊