His brain was just theirs. A．as full of

有4台设备，每台正常工作的概率均为0.9，则4台中至少有3台能正常工作的概率为______．（用小数作答）

There is _____ " k" and _____ "e" in the word "key".   [ ]

A. a, an    

B. a, a    

C. a, ／    

D. an, ／

   I'm not mistaken, Rio de Janeiro of Brazil was chosen as the host city for the 2016 Olympics.

A．If

B．As

C．Unless

D．Though

如果考虑精神分裂症，其妄想特点为

A．妄想内容离奇，逻辑荒谬

B．妄想有事实依据

C．妄想逐渐产生

D．妄想不伴有情绪改变

E．妄想内容不涉及安全和个人需要

设n个随机变量X₁，X₂，…，X_n，是独立同分布，且D(X_i)=σ²，

，则______．