数字货币可以认为是一种基于节点网络和数字加密算法的虚拟货币。数字货币的核心特征是：
A. 以上都是
B. 没有发行主体
C. 发行总量有限
D. 交易需要共同记录
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The cross-correlation function of two periodic signals with the same period 𝑇 _____ .
A. is a non-periodic signal
B. is also periodic with period 2T
C. is also periodic with period T/2
D. is also periodic with the same period 𝑇
Which scale of measurement can be used to describe the following relationship?A-B < C-D, A-B = C-D, A-B > C-D .
A. Distinctiveness
B. Absolute magnitude
C. Equal/unequal intervals
D. Ordering in magnitude
In STFT, a narrow window will lead to ____ .
A. Good frequency resolution, poor time resolution
B. Good frequency resolution, good time resolution
C. Poor frequency resolution, good time resolution
D. Poor frequency resolution, poor time resolution
Autocorrelation function is a (an) _____ function.
A. Even
B. Odd
C. Triangle
D. Nonodd and noneven
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