He was ____with his business matters and didn't have time to think about holiday.
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For the purpose of ____, We labeled each sample with a number.
In many cultures, eggs are an obvious symbol of new life, and the newborn chicks are a lovely ____of new growth.
有效值、频率和角频率是指正弦交流电的三要素。
A. 对
B. 错
正弦交流电常用的表示方法是函数式、波形图和相量图。
A. 对
B. 错
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