19. 已知随机变量ξ\xiξ服从正态分布N(2,σ2)N(2,\sigma ^{2})N(2,σ2),且P(ξ<3)=0.6P(\xi <3)=0.6P(ξ<3)=0.6,则P(1<ξ<2)=(P(1<\xi <2)=(P(1<ξ<2)=( )))