Area under normal curve within +- 1SD (standard detion)-: (A) 0.68, (B) 0.17, (C) 0.12, (D) 0.34
Answer is A. Ref:Parks 23rd edition pg 849. +/-1sd includes 68% i.e . 0.68 1SD : confidence limit = 68% 2SD : confidence limit = 95% 3SD : confidence limit = 99.7%