容量为32的样本,若某组样本频率为0.25,则该组的频数为( )
A.14
B.8
C.16
D.无法确定
该组样本的频数为32×0.25=8
则该组的频数为8.
故选B.
He left his hometown in 1990, and great changes _________ ever since.
A.had taken place
B.took place
C.have been take place
D.have taken place
()雷管通电后立即爆炸,允许在地面及任何瓦斯矿井中使用。
A.瞬发电雷管
B.毫秒延期雷管
C.秒延期雷管
D.延期雷管