铝合金人工时效比自然时效所获得的硬度高，且效率也高，因此多数情况下采用人工时效。
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发票领购簿属于税收执法类文书
A. 正确
B. 错误
电价按照生产流通环节划分可分为：①直供电价；②趸售电价；③互供电价。
A. 正确
B. 错误
主机曲轴箱滑油，一般的化验项目是（）①闪点、酸值；②灰分、凝点；③粘度、总碱值。
A. ①+②
B. ①+③
C. ②+③
D. ①+②+③
Which of the following statements is true regarding the installation of piston rings on two-stroke/cycle, diesel engines as compared to four-stroke/cycle, diesel engines?（）
A. In a two-stroke/cycle engine, the rings run hotter, requiring the end gap to be greater
B. Some provision must be made in a two-stroke/cycle engine to keep the rings from binding in the ports
C. No gap is required to exist between the ends of the ring when cold in a two-stroke/cycle engine, but a small gap is required in a four-stoke/cycle engine
D. The gaps should be staggered on either side of a piston in a two-stroke/cycle engine, while staggering is not necessary in a four-stroke/cycle engine
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