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【单选题】
下列各族元素中,金属的化学活泼性随原子序数增加而减弱的是 ( D ) 。A.
IA
B.
IIA
C.
IIIA
D.
IB
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反馈参考答案：
举一反三
【单选题】He told me he see me again before long.
A.
will come to
B.
is going to come
C.
would come to
D.
comes to
【简答题】（）是将总体各单位划分为若干群，然后以群为单位进行抽样，把中选群的所有单位都作为研究对象。
【单选题】He must have done it well, because he told me he just did what he _____ to do.
A.
has been told
B.
had been told
C.
was told
D.
had told
【简答题】当超声波从一种介质向另一种介质传播时,如果两者的声阻抗不同,就会在其分界面上产生________和________现象。
【单选题】——What did your uncle say？ ——He told me he call me the next day.
A.
will
B.
should
C.
would
【单选题】先将总体划分为若干群,然后以群作为抽样单位从中抽取部分群,再对抽中的各个群中所包含的所有元素进行观察,这样的抽样方式称为
A.
简单随机抽样
B.
分层抽样
C.
系统抽样
D.
整群抽样
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