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【单选题】
大小肺泡稳定性的维持,有赖于肺表面活性物质在A.
大肺泡内密度低，小肺泡内密度高。
B.
呼气时肺泡内的密度低。
C.
吸气时肺泡内的密度高。
D.
大小肺泡内的密度均低。
E.
大小肺泡内的密度于呼吸期中稳定不变。
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反馈参考答案：
举一反三
【单选题】He came to help us _____ he had plenty of work to do.
A.
as
B.
while
C.
although
D.
whenever
【单选题】Henry seldom came here to help us, _____?
A.
didn’t he
B.
doesn’t he
C.
dose he
D.
did he
【简答题】Before he came we had expected him to help us but when he was with us he didn't do much.
【简答题】He came to help us _________ he had plenty of
work to do.A. as B. while C. although D. whenever
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