求解网络函数时，储能元件无初始储能，其零状态响应与激励源的之比为网络函数。
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She asked John where he had been, but John didn't _____ .
A. reply
B. refer
C. agree
D. return
It is important _____ you should try to finish the project within 3 months.
A. whether
B. why
C. how
D. that
The film _____ next week is Avengers: Age of Ultron.
A. showing
B. to be shown
C. being shown
D. to have been shown
George called the airline to ______ his flight to London this morning.
A. improve
B. confirm
C. believe
D. insure
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