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【单选题】
下图是烟雾电子报警器的测试电路，烟雾浓度未超标时，下面说法哪种正确。【图片】A.
集成运放IC1A输出高电平，发光二极管VL9灭。
B.
集成运放IC1A输出高电平，发光二极管VL9亮。
C.
集成运放IC1A输出低电平，发光二极管VL9灭。
D.
集成运放IC1A输出低电平，发光二极管VL9亮。
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举一反三
【单选题】I ____ that we would be able to leave soon, but it’s beginning to look difficult.
A.
hoped
B.
have hoped
C.
was hoping
D.
had hoped
【单选题】I ______ that we would be able to leave tomorrow, but it's beginning to look difficult.
A.
hope
B.
hoped
C.
have hoped
D.
had hoped
【单选题】－I my keys in the room yesterday. I had to get in the window. －It’s dangerous to do that.
A.
leave, from
B.
left, through
C.
forget, from
D.
forgot, through
【单选题】—Excuse me, visiting hours are over．It' s time for you to leave． —I' m sorry, I didn't know the time or I ______ earlier．
A.
will leave
B.
would leave
C.
had left
D.
would have left
【单选题】I ______ that we would be able to leave tomorrow, but it's beginning to look difficult.
A.
had hoped
B.
has hoped
C.
hope
D.
hoped
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