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【单选题】
一束波长为λ的平行单色光垂直入射到一单缝AB上,装置如图.在屏幕D上形成衍射图样,如果P是中央亮纹一侧第一个暗纹所在的位置,则 的长度为A.
/2．
B.
．
C.
3 /2 ．
D.
2 ．
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举一反三
【单选题】The end sentence of the article is to ______.
A.
emphasize the importance of love
B.
explain how people love each other
C.
show why lovers exchange rings
D.
tell a story of rings in the universe
【单选题】The author's intention in writing the article is to make Americans realize that ______.
A.
it is dangerous to ignore their foreign friends
B.
it is important to maintain their leading role in world affairs
C.
it is necessary to use several languages in public places
D.
it is time to get acquainted with other cultures
【简答题】The purpose of the article is to explain_________
【单选题】The purpose of the article is to draw public attention ______ the problem.
A.
to
B.
on
C.
in
D.
for
【单选题】The aim of the article is to _____.
A.
show how to use smart cards.
B.
show the difference between ATM card and chip card.
C.
how the smart cards have become popular.
D.
persuade Americans to use smart cards.
【单选题】The purpose of the article is to tell us ______.
A.
the effect of antibiotics
B.
not to use antibiotics unless necessary
C.
that antibiotics are harmfull
D.
that our natural defence systems are superior to antibiotics
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