正弦交流电的周期、频率和角频率都是表示正弦交流电变化快慢的物理量，只要知道一个，就可以推算出另外两个。
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相量表示法中，相量的长度表示正弦交流电的最大值或有效值。
A. 对
B. 错
They made a new ______ to solve the problem, but failed again.
A. addition
B. attempt
C. platform
D. emphasis
It can be said that the adoption of shifting perspective is one of the ______ of Chinese painting.
A. characteristics
B. designs
C. imitations
D. feelings
His paintings often show some beautiful ______ of the trees in the lake.
A. restriction
B. function
C. reflection
D. observation
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