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【单选题】
某离散时间系统的差分方程为 a 0 y(n+2)+a 1 y(n+1)+a 2 y(n)+a 3 y(n-1)=b 1 x(n+1) ,该系统的阶次为 。A.
4
B.
3
C.
2
D.
1
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举一反三
【单选题】If the measures had been available, the doctors and patients ______ from SARS.
A.
could not have died
B.
should not have died
C.
wouldn't have died
D.
would not die
【单选题】The little boy was in danger. The doctors and nurses are doing him.
A.
what they can do help
B.
everything they can help
C.
what they can to help
D.
all what to help
【单选题】The patient’s dangerous condition ____the doctors and nurses many a sleepless night.
A.
cost
B.
spent
C.
paid
D.
made
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