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问题
单项选择题
工程中常见的周期信号其谐波的幅值随谐波的频率增加而（）
A.不变
B.减小
C.增加
D.不确定
答案
参考答案：
B
选择题
Mary did _______ her sister in the maths exam.
A. as worse as
B. more careful than
C. as good as
D. much more carelessly than
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问答题 简答题
密封油泵发生故障后应如何处理？
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