质量检验时,将总体按某一特性分为若干组,从每组中随机抽取样品组成样本的抽样方法称为()。
A.简单随机抽样
B.分层抽样
C.等距抽样
D.多阶段抽样
参考答案:B
有毒性的安神药是()。
A.酸枣仁
B.远志
C.磁石
D.朱砂
E.琥珀
As I waited for Mike to arrive, I ____ the clock and saw that he was late.
A.glanced at
B.stared at
C.watched
D.noticed