【单选题】(理)若随机变量的分布列如下表,则Eξ的值为( ) ξ? 0 1 2 3 4 5 P 2x 3x 7x 2x 3x x
【单选题】Why does the woman's initial excitement turn to disappointment?
A.
She is told that all swimming classes are full.
B.
She learns that she will have to pay extra for classes.
C.
She finds out that there are no swimming classes at her level.
D.
She thought all sports activities were supervised by coaches.
【判断题】三相半波可控整流电路,不需要用大于60o小于120o的宽脉冲触发,也不需要相隔60o的双脉冲触发,只用符合要求的相隔120o的三组脉冲触发就能正常。
【单选题】静脉注射硫喷妥钠作用维持时间短暂的主要原因是( )
【单选题】船长下达弃船的命令后______应按______完成各自的弃船准备工作
【单选题】Why does the man need the woman's help?
A.
Because he fell down into the deep bunker.
B.
Because he can't get the ball out of the deep bunker.
C.
Because he can't find his ball.
D.
Because he can't find his sand wedge.
【单选题】若随机变量X的分布列如下表,则E(X)=( ) X 0 1 2 3 4 5 P 2x 3x 7x 2x 3x x