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【单选题】
以下关于论证有效性的说法中，错误的是？A.
论证的有效性并不关心前提真假的问题。
B.
若一个论证是有效的，则前提为假时，结论必然为假。
C.
若一个论证是有效的，则前提为，结论必然为真。
D.
若一个论证是无效的，则前提为，结论有可能为假。
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【简答题】Spell the past tense of the word "magic".
【单选题】违反本法规定被吊销导游证的导游、领队和受到吊销旅行社业务经营许可证处罚的旅行社的有关管理人员,自处罚之日起未逾 的,不得重新申请导游证或者从事旅行社业务。
A.
一年
B.
二年
C.
三年
D.
四年
【单选题】No light ____ in the house for the past two evenings, one of the neighbors broke in and found the old lady in her chair.
A.
being visible
B.
to be visible
C.
has been visible
D.
having been visible
【单选题】The reason why there still needs improvement in the past view of Archaeopteryx is that
A.
fossils of those earliest birds haven't been discovered yet.
B.
the wishbone they studied is just so-called wishbone.
C.
there was no study of the role of its brain and some faculties in flight.
D.
Archaeopteryx is regarded as the earliest known bird.
【单选题】AIDS is said_______ the biggest health challenge to both men and women in the earth over the past four years.
A.
that it is
B.
to have been
C.
that it has been
D.
to be
【判断题】《旅游法》规定，被吊销导游证的导游、和收到吊销旅行社业务经营许可证处罚的旅行社的有关管理人员，自处罚之日起未逾两年的，不得重新申请导游证或者从事旅行社业务。
A.
正确
B.
错误
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