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【单选题】
I型呼衰吸氧浓度建议?A.
高浓度（＞65%）
B.
高浓度（＞35%）
C.
中高浓度（＞25%）
D.
低浓度（<35%）< /div>
E.
低浓度（<20%）< /div>
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举一反三
【单选题】The express railway between Beijing and Guangzhou was finished( ).
A.
at the end of this year
B.
before the New year of 2013
C.
after 2013
D.
in about 5 years
【简答题】Traveling by train is usually not easy in China. It can be hard to get a ticket. When you're traveling to the railway station you look at your watch, afraid you will miss your train. But there is good...
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