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【单选题】
在一测试系统中，被测信号频率为1000Hz，幅值为4V，另有两干扰信号分别为2000Hz，8V和500Hz，2V，则利用______提取有用信号。A.
叠加性
B.
比例性
C.
频率保持性
D.
幅值保持性
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举一反三
【单选题】He told me that he ____ in Naples the previous year.
A.
has been working
B.
has worked
C.
had been working
D.
had been worked
【简答题】A和B形成理想溶液，已知373K时纯A的蒸气压为133.32kPa，纯B的蒸气压为66.66kPa，与此二元形成平衡的气相中A的摩尔分数为2/3时，溶液中A的摩尔分数为（）
【单选题】—________ ! Somebody has left the lab door open. —Don’t look at me.
A.
Dear me
B.
Hi, there
C.
Thank goodness
D.
Come on
【单选题】______, John would not have failed．
A.
Has he listened to me
B.
If he listened to me
C.
Should he listen to me
D.
Had he listened to me
【单选题】若A和B形成理想液态混合物,已知 373K 时纯 A 的蒸气压为133.32 kPa,纯 B 的蒸气压为 66.66 kPa,此时二元溶液成平衡的气相中的 A 摩尔分数为 2/3 时,溶液中A的摩尔分数为( )。
A.
3/4
B.
2/3
C.
1/2
D.
1/4
【单选题】A和B形成理想溶液，已知373K时纯A的蒸气压为133.32kPa，纯B的蒸气压为66.66kPa，与此二元溶液成平衡的气相中的A摩尔分数为2/3时，溶液中A的摩尔分数为（）
A.
1
B.
2/3
C.
1/2
D.
1/4
【单选题】My dad hardly ever has time for concerts with me now, _______? [ ]
A.
has he
B.
hasn't he
C.
doesn't he
D.
does he
【单选题】He has promised me that upon my return he for me at the airport.
A.
is waiting
B.
will be waiting[
C.
will have waited
D.
waits
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