单项选择题

How did the science of preparing metals for use happen

A．By any planned purpose.
B．By chance.
C．With fire.
D．On the part of those who were concerned about it.
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单项选择题
According to the passage, background music is so widespread because it can ______.
A．help to create a soothing atmosphere
B．decrease production in factories
C．promote sales in all places
D．help to have more meals
单项选择题
From the passage, we know that ______.
A．music can be divided into slow music and fast music
B．whether slow music and fast music is effective or not depends on the background
C．music are always helpful to the overall sales
D．without music people have difficulty in shopping and having dinners
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