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产房中有四个婴儿同时啼哭,如果每个婴儿啼哭声音的声强级均为50dB,则四个婴儿同时啼哭的声强级是____________________ dB。(计算结果保留两位有效数字)

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Listen to the following sentences and fill in the blanks.(1)Without considerate____________________ and pricing decisions the e-shop owner may get into trouble.(2)Deciding which products to sell online can be quite a task and you need to take so many things into consideration such as _____________________, competition and profit.(3)Apparel and fashion, with its endless ________________ and relatively low shipping costs, is clearly a great category for new sellers to explore.(4)With your ____________________ you need to accommodate for competition dynamics, cultural factors, taste profiling, packing design, language, pricing and much more.(5)This e-commerce platform helps you purchase goods that are of great value and also offer an _______________________ .

使用万用表的电阻档测量线路的电阻,阻值为0时,代表线路( )

A. 断路
B. 短路

测量交流电压380V,使用万用表应选择的挡位是( )

AC 750V
B. AC 200V
C. AC 20V
D. AC 1000V

数字式万用表当选择电阻档测量电阻时,显示屏显示“1□□”,代表的含义是( )

A. 阻值为1欧姆
B. 阻值为无穷大

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