For a symmetrical distribution approximately 68% of the cases are included between _________________?

A. X¯¯¯¯−S and X¯¯¯¯+S
B. X¯¯¯¯−2S and X¯¯¯¯+2S
C. X¯¯¯¯−3S and X¯¯¯¯+3S
D. None of these