【单选题】下列四个判断: ① ; ②已知随机变量X服从正态分布N(3, ),P(X≤6)=0.72,则P(X≤0)=0.28; ③已知 的展开式的各项系数和为32,则展开式中x项的系数为20; ④ 其中正确的个数有:
【单选题】下列有关人群易感性的说法中正确的是 ( )
【单选题】It was no surprise when we were told that our grandfather had passed away.
【单选题】The fire had______when the firemen hurried there.
【简答题】以下关于行业的成熟期的说法不正确的是( )。