样本记录x(t)所有瞬时值的简单平均是随机信号的()。

A punctual person is in the habit of doing a thing at the【11】time and is never late in keeping an appointment. He knows that he can not get through his immense amount of work【12】he faithfully keeps every【13】promptly and deals with every piece of work【14】it has to be attended to. There is a【15】which says, 'Time flies, never to be recalled.' Time is more【16】than material things.The unpunctual man, on the other hand, never does what he has to do at the proper time. He is always【17】that he finds no time to answer letters, or return calls or keep appointments【18】. Friends sometimes grow cold towards each other, or even become enemies, because one of them has been remiss in answering letters or keeping appointments. Tile punctual man is a source of annoyance【19】to others and to himself. Unpunctuality, moreover, is very harmful when it comes to doing one' s duty, whether public or private. Failure to be punctual in【20】one' s appointments is a sign of disrespect towards others. A man who is known to be habitually unpunctual is never trusted by his friends or fellow men. In the end, he loses both time and his good name.(46) 点击查看答案

若x(t)的拉普拉斯变换为X(s)，且各阶导数(含零阶)的初始值均为零，则x(t)的一阶导数的拉普拉斯变换为()。

A、X(s)
B、S2X(s)
C、sX(s)
D、S3X(s)

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