题目内容

下列叙述正确的是（）

A. 两个连续周期信号的和一定是周期信号
B. 两个连续周期信号的周期之比为有理数时，其和信号才是周期信号，其周期是这两个周期信号周期的最小公倍数
C. 两个离散周期序列之和不一定是周期序列
D. 以上说法均不正确

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