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【单选题】
Application对象的默认有效期是（ ）？A.
20分钟
B.
10分钟
C.
20秒
D.
从应用程序启动到结束
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皮皮学刷刷变学霸
举一反三
【单选题】I'm sorry you've waited so long, but there will be some time _______ Bran gets back
A.
when
B.
since
C.
till
D.
after
【单选题】Why isnt it important what McKay sees in the machine?
A.
He doesn't like the machine.
B.
An eye chart is better.
C.
It's what the machine sees in him that is important.
D.
The prototype doesn't work very well.
【简答题】What should you do if a machine jams
【单选题】—We've waited for the two singers for two hours. Will they be able to come here? —I'm afraid ____ of them will come today. [ ]
A.
neither
B.
either
C.
both
D.
none
【单选题】—I've not finished with my dinner yet. —But our friends______for us.
A.
waited
B.
to be waited
C.
waiting
D.
are waiting
【单选题】---Did you wait for him long? ---No, I hadn’t waited long _______ he appeared.
A.
unless
B.
until
C.
before
D.
since
【简答题】lf a machine jams, take time to undo the jam or to tell the proper person to attend to it.
【简答题】用定义求下列函数的拉氏变换： (1)f(t)=e -2t (2)lf(t)=2t
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