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[单选题]
Then _____ of that time when he was cowboy
A. Comes the memory
B. came the memory
C. the memory comes
D. the memory came
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A. Comes the memory
B. came the memory
C. the memory comes
D. the memory came
已知f1(t)=tε(t),f2(t)=ε(t)-ε(t-2),求y(t)=f1(t)*f2(t-1)*δ'(t-2)。
A.mightn't
B.won't
C.needn't
D.mustn't
A.y’(t)/x(t)
B.-y’(t)/x(t)
C.y’(t)/x’(t)
D.y(t)/x’(t)
E.-y(t)/x’(t)
已知信号h(t)=ε(t一1)一ε(t一2),f(t)=ε(t一2)一ε(t一4),则卷积h(t)*f(t)=_____________。